XFree86 DDX Design

The XFree86 Project

The X.Org Foundation

Jim Gettys

   Updates for X11R6.7

   X Version 11, Release 7.7

   X Server Version 1.19.6

   2017-12-20
     __________________________________________________________

   Table of Contents

   Preface
   The xorg.conf File

        Device section
        Screen section
        InputDevice section
        ServerLayout section
        Options

   Driver Interface
   Resource Access Control Introduction

        Terms and Definitions

   Control Flow in the Server and Mandatory Driver Functions

        Parse the xorg.conf file
        Initial processing of parsed information and command line
                options

        Enable port I/O access
        General bus probe
        Load initial set of modules
        Register Video and Input Drivers
        Initialise Access Control
        Video Driver Probe
        Matching Screens
        Allocate non-conflicting resources
        Sort the Screens and pre-check Monitor Information
        PreInit
        Cleaning up Unused Drivers
        Consistency Checks
        Check if Resource Control is Needed
        AddScreen (ScreenInit)
        Finalising RAC Initialisation
        Finishing InitOutput()
        Mode Switching
        Changing Viewport
        VT Switching
        End of server generation

   Optional Driver Functions

        Mode Validation
        Free screen data

   Recommended driver functions

        Save
        Restore
        Initialise Mode

   Data and Data Structures

        Command line data
        Data handling
        Accessing global data
        Allocating private data

   Keeping Track of Bus Resources

        Theory of Operation
        Resource Types
        Available Functions

   Config file “Option” entries
   Modules, Drivers, Include Files and Interface Issues

        Include files

   Offscreen Memory Manager
   Colormap Handling
   DPMS Extension
   DGA Extension
   The XFree86 X Video Extension (Xv) Device Dependent Layer
   The Loader

        Loader Overview
        Semi-private Loader Interface
        Module Requirements
        Public Loader Interface
        Special Registration Functions

   Helper Functions

        Functions for printing messages
        Functions for setting values based on command line and
                config file

        Primary Mode functions
        Secondary Mode functions
        Functions for handling strings and tokens
        Functions for finding which config file entries to use
        Probing discrete clocks on old hardware
        Other helper functions

   The vgahw module

        Data Structures
        General vgahw Functions
        VGA Colormap Functions
        VGA Register Access Functions

   Some notes about writing a driver

        Include files
        Data structures and initialisation
        Functions

Note

   This document describes software undergoing continual
   evolution, and the interfaces described here are subject to
   change without notice. This document is intended to cover the
   interfaces as found in the xorg-server-1.19.6 release, but is
   probably not completely in sync with the code base.

Preface

   This document was originally the design spec for the DDX layer
   of the XFree86 4.0 X server. The X.Org Foundation adopted the
   XFree86 4.4rc2 version of that server as the basis of the Xorg
   server project, and has evolved the XFree86 DDX layer greatly
   since forking. This document thus covers only the current
   implementation of the XFree86 DDX as found in the Xorg server
   1.19.6 release, and no longer matches the XFree86 server
   itself.

   The XFree86 Project's broad design principles for XFree86 4.0
   were:
     * keep it reasonable
          + We cannot rewrite the complete server
          + We don't want to re-invent the wheel
     * keep it modular
          + As many things as possible should go into modules
          + The basic loader binary should be minimal
          + A clean design with well defined layering is important
          + DDX specific global variables are a nono
          + The structure should be flexible enough to allow
            future extensions
          + The structure should minimize duplication of common
            code
     * keep important features in mind
          + multiple screens, including multiple instances of
            drivers
          + mixing different color depths and visuals on different
            and ideally even on the same screen
          + better control of the PCI device used
          + better config file parser
          + get rid of all VGA compatibility assumptions

   While the XFree86 project had a goal of avoiding changes to the
   DIX layer unless they found major deficiencies there, to avoid
   divergence from the X.Org sample implementation they were
   integrating changes from, the X.Org developers now maintain
   both sides, and make changes where they are most appropriate.
   This document concentrates on the XFree86 DDX layer used in the
   Xorg server itself (the code found in hw/xfree86 in the source
   tree), and developers will also want to refer to the
   Xserver-spec documentation that covers the DIX layer routines
   common to all the X servers in the sample implementation.

The xorg.conf File

   The xorg.conf file format is based on the XF86Config format
   from XFree86 4.4, which is in turn similar to the old XFree86
   3.x XF86Config format, with the following changes:

Device section

   The Device sections are similar to what they used to be, and
   describe hardware-specific information for a single video card.
   Device Some new keywords are added:

   Driver "drivername"

   Specifies the name of the driver to be used for the card. This
   is mandatory.

   BusID "busslot"

   Specifies uniquely the location of the card on the bus. The
   purpose is to identify particular cards in a multi-headed
   configuration. The format of the argument is intentionally
   vague, and may be architecture dependent. For a PCI bus, it is
   something like "bus:slot:func".

   A Device section is considered “active” if there is a reference
   to it in an active Screen section.

Screen section

   The Screen sections are similar to what they used to be. They
   no longer have a Driver keyword, but an Identifier keyword is
   added. (The Driver keyword may be accepted in place of the
   Identifier keyword for compatibility purposes.) The identifier
   can be used to identify which screen is to be active when
   multiple Screen sections are present. It is possible to specify
   the active screen from the command line. A default is chosen in
   the absence of one being specified. A Screen section is
   considered “active” if there is a reference to it either from
   the command line, or from an active ServerLayout section.

InputDevice section

   The InputDevice section is a new section that describes
   configuration information for input devices. It replaces the
   old Keyboard, Pointer and XInput sections. Like the Device
   section, it has two mandatory keywords: Identifier and Driver.
   For compatibility purposes the old Keyboard and Pointer
   sections are converted by the parser into InputDevice sections
   as follows:

   Keyboard

                        Identifier "Implicit Core Keyboard"
                        Driver "kbd"

   Pointer

                        Identifier "Implicit Core Pointer"
                        Driver "mouse"

   An InputDevice section is considered active if there is a
   reference to it in an active ServerLayout section. An
   InputDevice section may also be referenced implicitly if there
   is no ServerLayout section, if the -screen command line options
   is used, or if the ServerLayout section doesn't reference any
   InputDevice sections. In this case, the first sections with
   drivers "kbd" and "mouse" are used as the core keyboard and
   pointer respectively.

ServerLayout section

   The ServerLayout section is a new section that is used to
   identify which Screen sections are to be used in a multi-headed
   configuration, and the relative layout of those screens. It
   also identifies which InputDevice sections are to be used. Each
   ServerLayout section has an identifier, a list of Screen
   section identifiers, and a list of InputDevice section
   identifiers. ServerFlags options may also be included in a
   ServerLayout section, making it possible to override the global
   values in the ServerFlags section.

   A ServerLayout section can be made active by being referenced
   on the command line. In the absence of this, a default will be
   chosen (the first one found). The screen names may optionally
   be followed by a number specifying the preferred screen number,
   and optionally by information specifying the physical
   positioning of the screen, either in absolute terms or relative
   to another screen (or screens). When no screen number is
   specified, they are numbered according to the order in which
   they are listed. The old (now obsolete) method of providing the
   positioning information is to give the names of the four
   adjacent screens. The order of these is top, bottom, left,
   right. Here is an example of a ServerLayout section for two
   screens using the old method, with the second located to the
   right of the first:
      Section "ServerLayout"
        Identifier "Main Layout"
        Screen     0 "Screen 1" ""  ""  ""  "Screen 2"
        Screen     1 "Screen 2"
        Screen     "Screen 3"
      EndSection

   The preferred way of specifying the layout is to explicitly
   specify the screen's location in absolute terms or relative to
   another screen.

   In the absolute case, the upper left corner's coordinates are
   given after the Absolute keyword. If the coordinates are
   omitted, a value of (0,0) is assumed. An example of absolute
   positioning follows:
      Section "ServerLayout"
        Identifier "Main Layout"
        Screen     0 "Screen 1" Absolute 0 0
        Screen     1 "Screen 2" Absolute 1024 0
        Screen     "Screen 3" Absolute 2048 0
      EndSection

   In the relative case, the position is specified by either using
   one of the following keywords followed by the name of the
   reference screen:
   RightOf
   LeftOf
   Above
   Below
   Relative

   When the Relative keyword is used, the reference screen name is
   followed by the coordinates of the new screen's origin relative
   to reference screen. The following example shows how to use
   some of the relative positioning options.
      Section "ServerLayout"
        Identifier "Main Layout"
        Screen     0 "Screen 1"
        Screen     1 "Screen 2" RightOf "Screen 1"
        Screen     "Screen 3" Relative "Screen 1" 2048 0
      EndSection

Options

   Options are used more extensively. They may appear in most
   sections now. Options related to drivers can be present in the
   Screen, Device and Monitor sections and the Display
   subsections. The order of precedence is Display, Screen,
   Monitor, Device. Options have been extended to allow an
   optional value to be specified in addition to the option name.
   For more details about options, see the Options section for
   details.

Driver Interface

   The driver interface consists of a minimal set of entry points
   that are required based on the external events that the driver
   must react to. No non-essential structure is imposed on the way
   they are used beyond that. This is a significant difference
   compared with the old design.

   The entry points for drawing operations are already taken care
   of by the framebuffer code. Extensions and enhancements to
   framebuffer code are outside the scope of this document.

   This approach to the driver interface provides good
   flexibility, but does increase the complexity of drivers. To
   help address this, the XFree86 common layer provides a set of
   “helper” functions to take care of things that most drivers
   need. These helpers help minimise the amount of code
   duplication between drivers. The use of helper functions by
   drivers is however optional, though encouraged. The basic
   philosophy behind the helper functions is that they should be
   useful to many drivers, that they should balance this against
   the complexity of their interface. It is inevitable that some
   drivers may find some helpers unsuitable and need to provide
   their own code.

   Events that a driver needs to react to are:

   ScreenInit

   An initialisation function is called from the DIX layer for
   each screen at the start of each server generation.

   Enter VT

   The server takes control of the console.

   Leave VT

   The server releases control of the console.

   Mode Switch

   Change video mode.

   ViewPort change

   Change the origin of the physical view port.

   ScreenSaver state change

   Screen saver activation/deactivation.

   CloseScreen

   A close screen function is called from the DIX layer for each
   screen at the end of each server generation.

   In addition to these events, the following functions are
   required by the XFree86 common layer:

 Identify

         Print a driver identifying message.

 Probe

         This is how a driver identifies if there is any hardware
         present that it knows how to drive.

 PreInit

         Process information from the xorg.conf file, determine the full
         characteristics of the hardware, and determine if a valid
         configuration is present.

   The VidMode extension also requires:

  ValidMode

           Identify if a new mode is usable with the current
           configuration. The PreInit function (and/or helpers it calls)
           may also make use of the ValidMode function or something
           similar.

   Other extensions may require other entry points. The drivers
   will inform the common layer of these in such cases.

Resource Access Control Introduction

   Graphics devices are accessed through ranges in I/O or memory
   space. While most modern graphics devices allow relocation of
   such ranges many of them still require the use of well
   established interfaces such as VGA memory and IO ranges or
   8514/A IO ranges. With modern buses (like PCI) it is possible
   for multiple video devices to share access to these resources.
   The RAC (Resource Access Control) subsystem provides a
   mechanism for this.

Terms and Definitions

Bus

   “Bus” is ambiguous as it is used for different things: it may
   refer to physical incompatible extension connectors in a
   computer system. The RAC system knows two such systems: The ISA
   bus and the PCI bus. (On the software level EISA, MCA and VL
   buses are currently treated like ISA buses). “Bus” may also
   refer to logically different entities on a single bus system
   which are connected via bridges. A PCI system may have several
   distinct PCI buses connecting each other by PCI-PCI bridges or
   to the host CPU by HOST-PCI bridges.

   Systems that host more than one bus system link these together
   using bridges. Bridges are a concern to RAC as they might block
   or pass specific resources. PCI-PCI bridges may be set up to
   pass VGA resources to the secondary bus. PCI-ISA buses pass any
   resources not decoded on the primary PCI bus to the ISA bus.
   This way VGA resources (although exclusive on the ISA bus) can
   be shared by ISA and PCI cards. Currently HOST-PCI bridges are
   not yet handled by RAC as they require specific drivers.

Entity

   The smallest independently addressable unit on a system bus is
   referred to as an entity. So far we know ISA and PCI entities.
   PCI entities can be located on the PCI bus by an unique ID
   consisting of the bus, card and function number.

Resource

   “Resource” refers to a range of memory or I/O addresses an
   entity can decode.

   If a device is capable of disabling this decoding the resource
   is called sharable. For PCI devices a generic method is
   provided to control resource decoding. Other devices will have
   to provide a device specific function to control decoding.

   If the entity is capable of decoding this range at a different
   location this resource is considered relocatable.

   Resources which start at a specific address and occupy a single
   continuous range are called block resources.

   Alternatively resource addresses can be decoded in a way that
   they satisfy the conditions:
                    address & mask == base

   and
                       base & mask == base

   Resources addressed in such a way are called sparse resources.

Server States

   The resource access control system knows two server states: the
   SETUP and the OPERATING state. The SETUP state is entered
   whenever a mode change takes place or the server exits or does
   VT switching. During this state all entity resources are under
   resource access control. During OPERATING state only those
   entities are controlled which actually have shared resources
   that conflict with others.

Control Flow in the Server and Mandatory Driver Functions

   At the start of each server generation, main() (dix/main.c)
   calls the DDX function InitOutput(). This is the first place
   that the DDX gets control. InitOutput() is expected to fill in
   the global screenInfo struct, and one screenInfo.screen[] entry
   for each screen present. Here is what InitOutput() does:

Parse the xorg.conf file

   This is done at the start of the first server generation only.

   The xorg.conf file is read in full, and the resulting
   information stored in data structures. None of the parsed
   information is processed at this point. The parser data
   structures are opaque to the video drivers and to most of the
   common layer code.

   The entire file is parsed first to remove any section ordering
   requirements.

Initial processing of parsed information and command line options

   This is done at the start of the first server generation only.

   The initial processing is to determine paths like the
   ModulePath, etc, and to determine which ServerLayout, Screen
   and Device sections are active.

Enable port I/O access

   Port I/O access is controlled from the XFree86 common layer,
   and is “all or nothing”. It is enabled prior to calling driver
   probes, at the start of subsequent server generations, and when
   VT switching back to the Xserver. It is disabled at the end of
   server generations, and when VT switching away from the
   Xserver.

   The implementation details of this may vary on different
   platforms.

General bus probe

   This is done at the start of the first server generation only.

   In the case of ix86 machines, this will be a general PCI probe.
   The full information obtained here will be available to the
   drivers. This information persists for the life of the Xserver.
   In the PCI case, the PCI information for all video cards found
   is available by calling xf86GetPciVideoInfo().

    pciVideoPtr *xf86GetPciVideoInfo(void);

     returns a pointer to a list of pointers to pciVideoRec
     entries, of which there is one for each detected PCI video
     card. The list is terminated with a NULL pointer. If no PCI
     video cards were detected, the return value is NULL.

   After the bus probe, the resource broker is initialised.

Load initial set of modules

   This is done at the start of the first server generation only.

   The next set of modules loaded are those specified explicitly
   in the Module section of the config file.

   The final set of initial modules are the driver modules
   referenced by the active Device and InputDevice sections in the
   config file. Each of these modules is loaded exactly once.

Register Video and Input Drivers

   This is done at the start of the first server generation only.

   When a driver module is loaded, the loader calls its Setup
   function. For video drivers, this function calls
   xf86AddDriver() to register the driver's DriverRec, which
   contains a small set of essential details and driver entry
   points required during the early phase of InitOutput().
   xf86AddDriver() adds it to the global xf86DriverList[] array.

   The DriverRec contains the driver canonical name, the
   Identify(), Probe() and AvailableOptions() function entry
   points as well as a pointer to the driver's module (as returned
   from the loader when the driver was loaded) and a reference
   count which keeps track of how many screens are using the
   driver. The entry driver entry points are those required prior
   to the driver allocating and filling in its ScrnInfoRec.

   For a static server, the xf86DriverList[] array is initialised
   at build time, and the loading of modules is not done.

   A similar procedure is used for input drivers. The input
   driver's Setup function calls xf86AddInputDriver() to register
   the driver's InputDriverRec, which contains a small set of
   essential details and driver entry points required during the
   early phase of InitInput(). xf86AddInputDriver() adds it to the
   global xf86InputDriverList[] array. For a static server, the
   xf86InputDriverList[] array is initialised at build time.

   Both the xf86DriverList[] and xf86InputDriverList[] arrays have
   been initialised by the end of this stage.

   Once all the drivers are registered, their ChipIdentify()
   functions are called.

    void ChipIdentify(int flags);

     This is expected to print a message indicating the driver
     name, a short summary of what it supports, and a list of the
     chipset names that it supports. It may use the
     xf86PrintChipsets() helper to do this.

    void xf86PrintChipsets(const char *drvname, const char *drvmsg,
                           SymTabPtr chips);

     This function provides an easy way for a driver's
     ChipIdentify function to format the identification message.

Initialise Access Control

   This is done at the start of the first server generation only.

   The Resource Access Control (RAC) subsystem is initialised
   before calling any driver functions that may access hardware.
   All generic bus information is probed and saved (for
   restoration later). All (shared resource) video devices are
   disabled at the generic bus level, and a probe is done to find
   the “primary” video device. These devices remain disabled for
   the next step.

Video Driver Probe

   This is done at the start of the first server generation only.
   The ChipProbe() function of each registered video driver is
   called.

    Bool ChipProbe(DriverPtr drv, int flags);

     The purpose of this is to identify all instances of hardware
     supported by the driver. The flags value is currently either
     0, PROBE_DEFAULT or PROBE_DETECT. PROBE_DETECT is used if
     "-configure" or "-probe" command line arguments are given
     and indicates to the Probe() function that it should not
     configure the bus entities and that no xorg.conf information
     is available.

     The probe must find the active device sections that match
     the driver by calling xf86MatchDevice(). The number of
     matches found limits the maximum number of instances for
     this driver. If no matches are found, the function should
     return FALSE immediately.

     Devices that cannot be identified by using
     device-independent methods should be probed at this stage
     (keeping in mind that access to all resources that can be
     disabled in a device-independent way are disabled during
     this phase). The probe must be a minimal probe. It should
     just determine if there is a card present that the driver
     can drive. It should use the least intrusive probe methods
     possible. It must not do anything that is not essential,
     like probing for other details such as the amount of memory
     installed, etc. It is recommended that the
     xf86MatchPciInstances() helper function be used for
     identifying matching PCI devices, and similarly the
     xf86MatchIsaInstances() for ISA (non-PCI) devices (see the
     RAC section). These helpers also checks and claims the
     appropriate entity. When not using the helper, that should
     be done with xf86CheckPciSlot() and xf86ClaimPciSlot() for
     PCI devices and xf86ClaimIsaSlot() for ISA devices (see the
     RAC section).

     The probe must register all non-relocatable resources at
     this stage. If a resource conflict is found between
     exclusive resources the driver will fail immediately. This
     is usually best done with the xf86ConfigPciEntity() helper
     function for PCI and xf86ConfigIsaEntity() for ISA (see the
     RAC section). It is possible to register some entity
     specific functions with those helpers. When not using the
     helpers, the xf86AddEntityToScreen()
     xf86ClaimFixedResources() and xf86SetEntityFuncs() should be
     used instead (see the RAC section).

     If a chipset is specified in an active device section which
     the driver considers relevant (ie it has no driver
     specified, or the driver specified matches the driver doing
     the probe), the Probe must return FALSE if the chipset
     doesn't match one supported by the driver.

     If there are no active device sections that the driver
     considers relevant, it must return FALSE.

     Allocate a ScrnInfoRec for each active instance of the
     hardware found, and fill in the basic information, including
     the other driver entry points. This is best done with the
     xf86ConfigIsaEntity() helper function for ISA instances or
     xf86ConfigPciEntity() for PCI instances. These functions
     allocate a ScrnInfoRec for active entities. Optionally
     xf86AllocateScreen() function may also be used to allocate
     the ScrnInfoRec. Any of these functions take care of
     initialising fields to defined “unused” values.

     Claim the entities for each instance of the hardware found.
     This prevents other drivers from claiming the same hardware.

     Must leave hardware in the same state it found it in, and
     must not do any hardware initialisation.

     All detection can be overridden via the config file, and
     that parsed information is available to the driver at this
     stage.

     Returns TRUE if one or more instances are found, and FALSE
     otherwise.

    int xf86MatchDevice(const char *drivername,
                        GDevPtr **driversectlist)

     This function takes the name of the driver and returns via
     driversectlist a list of device sections that match the
     driver name. The function return value is the number of
     matches found. If a fatal error is encountered the return
     value is -1.

     The caller should use xfree() to free *driversectlist when
     it is no longer needed.

    ScrnInfoPtr xf86AllocateScreen(DriverPtr drv, int flags)

     This function allocates a new ScrnInfoRec in the
     xf86Screens[] array. This function is normally called by the
     video driver ChipProbe() functions. The return value is a
     pointer to the newly allocated ScrnInfoRec. The scrnIndex,
     origIndex, module and drv fields are initialised. The
     reference count in drv is incremented. The storage for any
     currently allocated “privates” pointers is also allocated
     and the privates field initialised (the privates data is of
     course not allocated or initialised). This function never
     returns on failure. If the allocation fails, the server
     exits with a fatal error. The flags value is not currently
     used, and should be set to zero.

   At the completion of this, a list of ScrnInfoRecs have been
   allocated in the xf86Screens[] array, and the associated
   entities and fixed resources have been claimed. The following
   ScrnInfoRec fields must be initialised at this point:

             driverVersion
             driverName
             scrnIndex(*)
             origIndex(*)
             drv(*)
             module(*)
             name
             Probe
             PreInit
             ScreenInit
             EnterVT
             LeaveVT
             numEntities
             entityList
             access

   (*) These are initialised when the ScrnInfoRec is allocated,
   and not explicitly by the driver.

   The following ScrnInfoRec fields must be initialised if the
   driver is going to use them:

             SwitchMode
             AdjustFrame
             FreeScreen
             ValidMode

Matching Screens

   This is done at the start of the first server generation only.

   After the Probe phase is finished, there will be some number of
   ScrnInfoRecs. These are then matched with the active Screen
   sections in the xorg.conf, and those not having an active
   Screen section are deleted. If the number of remaining screens
   is 0, InitOutput() sets screenInfo.numScreens to 0 and returns.

   At this point the following fields of the ScrnInfoRecs must be
   initialised:

             confScreen

Allocate non-conflicting resources

   This is done at the start of the first server generation only.

   Before calling the drivers again, the resource information
   collected from the Probe phase is processed. This includes
   checking the extent of PCI resources for the probed devices,
   and resolving any conflicts in the relocatable PCI resources.
   It also reports conflicts, checks bus routing issues, and
   anything else that is needed to enable the entities for the
   next phase.

   If any drivers registered an EntityInit() function during the
   Probe phase, then they are called here.

Sort the Screens and pre-check Monitor Information

   This is done at the start of the first server generation only.

   The list of screens is sorted to match the ordering requested
   in the config file.

   The list of modes for each active monitor is checked against
   the monitor's parameters. Invalid modes are pruned.

PreInit

   This is done at the start of the first server generation only.

   For each ScrnInfoRec, enable access to the screens entities and
   call the ChipPreInit() function.

    Bool ChipPreInit(ScrnInfoRec screen, int flags);

     The purpose of this function is to find out all the
     information required to determine if the configuration is
     usable, and to initialise those parts of the ScrnInfoRec
     that can be set once at the beginning of the first server
     generation.

     The number of entities registered for the screen should be
     checked against the expected number (most drivers expect
     only one). The entity information for each of them should be
     retrieved (with xf86GetEntityInfo()) and checked for the
     correct bus type and that none of the sharable resources
     registered during the Probe phase was rejected.

     Access to resources for the entities that can be controlled
     in a device-independent way are enabled before this function
     is called. If the driver needs to access any resources that
     it has disabled in an EntityInit() function that it
     registered, then it may enable them here providing that it
     disables them before this function returns.

     This includes probing for video memory, clocks, ramdac, and
     all other HW info that is needed. It includes determining
     the depth/bpp/visual and related info. It includes
     validating and determining the set of video modes that will
     be used (and anything that is required to determine that).

     This information should be determined in the least intrusive
     way possible. The state of the HW must remain unchanged by
     this function. Although video memory (including MMIO) may be
     mapped within this function, it must be unmapped before
     returning. Driver specific information should be stored in a
     structure hooked into the ScrnInfoRec's driverPrivate field.
     Any other modules which require persistent data (ie data
     that persists across server generations) should be
     initialised in this function, and they should allocate a
     “privates” index to hook their data into by calling
     xf86AllocateScrnInfoPrivateIndex(). The “privates” data is
     persistent.

     Helper functions for some of these things are provided at
     the XFree86 common level, and the driver can choose to make
     use of them.

     All additional resources that the screen needs must be
     registered here. This should be done with
     xf86RegisterResources(). If some of the fixed resources
     registered in the Probe phase are not needed or not decoded
     by the hardware when in the OPERATING server state, their
     status should be updated with xf86SetOperatingState().

     Modules may be loaded at any point in this function, and all
     modules that the driver will need must be loaded before the
     end of this function. Either the xf86LoadSubModule() or the
     xf86LoadDrvSubModule() function should be used to load
     modules depending on whether a ScrnInfoRec has been set up.
     A driver may unload a module within this function if it was
     only needed temporarily, and the xf86UnloadSubModule()
     function should be used to do that. Otherwise there is no
     need to explicitly unload modules because the loader takes
     care of module dependencies and will unload submodules
     automatically if/when the driver module is unloaded.

     The bulk of the ScrnInfoRec fields should be filled out in
     this function.

     ChipPreInit() returns FALSE when the configuration is
     unusable in some way (unsupported depth, no valid modes, not
     enough video memory, etc), and TRUE if it is usable.

     It is expected that if the ChipPreInit() function returns
     TRUE, then the only reasons that subsequent stages in the
     driver might fail are lack or resources (like xalloc
     failures). All other possible reasons for failure should be
     determined by the ChipPreInit() function.

   The ScrnInfoRecs for screens where the ChipPreInit() fails are
   removed. If none remain, InitOutput() sets
   screenInfo.numScreens to 0 and returns.

   At this point, further fields of the ScrnInfoRecs would
   normally be filled in. Most are not strictly mandatory, but
   many are required by other layers and/or helper functions that
   the driver may choose to use. The documentation for those
   layers and helper functions indicates which they require.

   The following fields of the ScrnInfoRecs should be filled in if
   the driver is going to use them:

             monitor
             display
             depth
             pixmapBPP
             bitsPerPixel
             weight                (>8bpp only)
             mask                  (>8bpp only)
             offset                (>8bpp only)
             rgbBits               (8bpp only)
             gamma
             defaultVisual
             maxHValue
             maxVValue
             virtualX
             virtualY
             displayWidth
             frameX0
             frameY0
             frameX1
             frameY1
             zoomLocked
             modePool
             modes
             currentMode
             progClock             (TRUE if clock is programmable)
             chipset
             ramdac
             clockchip
             numClocks             (if not programmable)
             clock[]               (if not programmable)
             videoRam
             biosBase
             memBase
             memClk
             driverPrivate
             chipID
             chipRev

    pointer xf86LoadSubModule(ScrnInfoPtr pScrn, const char *name);
      and
    pointer xf86LoadDrvSubModule(DriverPtr drv, const char *name);

     Load a module that a driver depends on. This function loads
     the module name as a sub module of the driver. The return
     value is a handle identifying the new module. If the load
     fails, the return value will be NULL. If a driver needs to
     explicitly unload a module it has loaded in this way, the
     return value must be saved and passed to
     xf86UnloadSubModule() when unloading.

    void xf86UnloadSubModule(pointer module);

     Unloads the module referenced by module. module should be a
     pointer returned previously by xf86LoadSubModule() or
     xf86LoadDrvSubModule() .

Cleaning up Unused Drivers

   At this point it is known which screens will be in use, and
   which drivers are being used. Unreferenced drivers (and modules
   they may have loaded) are unloaded here.

Consistency Checks

   The parameters that must be global to the server, like pixmap
   formats, bitmap bit order, bitmap scanline unit and image byte
   order are compared for each of the screens. If a mismatch is
   found, the server exits with an appropriate message.

Check if Resource Control is Needed

   Determine if resource access control is needed. This is the
   case if more than one screen is used. If necessary the RAC
   wrapper module is loaded.

AddScreen (ScreenInit)

   At this point, the valid screens are known. AddScreen() is
   called for each of them, passing ChipScreenInit() as the
   argument. AddScreen() is a DIX function that allocates a new
   screenInfo.screen[] entry (aka pScreen), and does some basic
   initialisation of it. It then calls the ChipScreenInit()
   function, with pScreen as one of its arguments. If
   ChipScreenInit() returns FALSE, AddScreen() returns -1.
   Otherwise it returns the index of the screen. AddScreen()
   should only fail because of programming errors or failure to
   allocate resources (like memory). All configuration problems
   should be detected BEFORE this point.

    Bool ChipScreenInit(ScreenPtr pScreen,
                        int argc, char **argv);

     This is called at the start of each server generation.

     Fill in all of pScreen, possibly doing some of this by
     calling ScreenInit functions from other layers like mi,
     framebuffers (cfb, etc), and extensions.

     Decide which operations need to be placed under resource
     access control. The classes of operations are the frame
     buffer operations (RAC_FB), the pointer operations
     (RAC_CURSOR), the viewport change operations (RAC_VIEWPORT)
     and the colormap operations (RAC_COLORMAP). Any operation
     that requires resources which might be disabled during
     OPERATING state should be set to use RAC. This can be
     specified separately for memory and IO resources (the
     racMemFlags and racIoFlags fields of the ScrnInfoRec
     respectively).

     Map any video memory or other memory regions.

     Save the video card state. Enough state must be saved so
     that the original state can later be restored.

     Initialise the initial video mode. The ScrnInfoRec's vtSema
     field should be set to TRUE just prior to changing the video
     hardware's state.

   The ChipScreenInit() function (or functions from other layers
   that it calls) should allocate entries in the ScreenRec's
   devPrivates area by calling AllocateScreenPrivateIndex() if it
   needs per-generation storage. Since the ScreenRec's devPrivates
   information is cleared for each server generation, this is the
   correct place to initialise it.

   After AddScreen() has successfully returned, the following
   ScrnInfoRec fields are initialised:

             pScreen
             racMemFlags
             racIoFlags

   The ChipScreenInit() function should initialise the CloseScreen
   and SaveScreen fields of pScreen. The old value of
   pScreen->CloseScreen should be saved as part of the driver's
   per-screen private data, allowing it to be called from
   ChipCloseScreen(). This means that the existing CloseScreen()
   function is wrapped.

Finalising RAC Initialisation

   After all the ChipScreenInit() functions have been called, each
   screen has registered its RAC requirements. This information is
   used to determine which shared resources are requested by more
   than one driver and set the access functions accordingly. This
   is done following these rules:
    1. The sharable resources registered by each entity are
       compared. If a resource is registered by more than one
       entity the entity will be marked to indicate that it needs
       to share this resources type (IO or MEM).
    2. A resource marked “disabled” during OPERATING state will be
       ignored entirely.
    3. A resource marked “unused” will only conflict with an
       overlapping resource of an other entity if the second is
       actually in use during OPERATING state.
    4. If an “unused” resource was found to conflict but the
       entity does not use any other resource of this type the
       entire resource type will be disabled for that entity.

Finishing InitOutput()

   At this point InitOutput() is finished, and all the screens
   have been setup in their initial video mode.

Mode Switching

   When a SwitchMode event is received, ChipSwitchMode() is called
   (when it exists):

    Bool ChipSwitchMode(int index, DisplayModePtr mode);

     Initialises the new mode for the screen identified by
     index;. The viewport may need to be adjusted also.

Changing Viewport

   When a Change Viewport event is received, ChipAdjustFrame() is
   called (when it exists):

    void ChipAdjustFrame(int index, int x, int y);

     Changes the viewport for the screen identified by index;.

     It should be noted that many chipsets impose restrictions on
     where the viewport may be placed in the virtual resolution,
     either for alignment reasons, or to prevent the start of the
     viewport from being positioned within a pixel (as can happen
     in a 24bpp mode). After calculating the value the chipset's
     panning registers need to be set to for non-DGA modes, this
     function should recalculate the ScrnInfoRec's frameX0,
     frameY0, frameX1 and frameY1 fields to correspond to that
     value. If this is not done, switching to another mode might
     cause the position of a hardware cursor to change.

VT Switching

   When a VT switch event is received, xf86VTSwitch() is called.
   xf86VTSwitch() does the following:

   On ENTER:
              * enable port I/O access
              * save and initialise the bus/resource state
              * enter the SETUP server state
              * calls ChipEnterVT() for each screen
              * enter the OPERATING server state
              * validate GCs
              * Restore fb from saved pixmap for each screen
              * Enable all input devices

   On LEAVE:
              * Save fb to pixmap for each screen
              * validate GCs
              * enter the SETUP server state
              * calls ChipLeaveVT() for each screen
              * disable all input devices
              * restore bus/resource state
              * disables port I/O access

    Bool ChipEnterVT(ScrnInfoPtr pScrn);

     This function should initialise the current video mode and
     initialise the viewport, turn on the HW cursor if
     appropriate, etc.

     Should it re-save the video state before initialising the
     video mode?

    void ChipLeaveVT(ScrnInfoPtr pScrn);

     This function should restore the saved video state. If
     appropriate it should also turn off the HW cursor, and
     invalidate any pixmap/font caches.

   Optionally, ChipLeaveVT() may also unmap memory regions. If so,
   ChipEnterVT() will need to remap them. Additionally, if an
   aperture used to access video memory is unmapped and remapped
   in this fashion, ChipEnterVT() will also need to notify the
   framebuffer layers of the aperture's new location in virtual
   memory. This is done with a call to the screen's
   ModifyPixmapHeader() function, as follows

    (*pScreen->ModifyPixmapHeader)(pScrn->ppix,
                                   -1, -1, -1, -1, -1, NewApertureAddres
s);

     where the ppix field in a ScrnInfoRec points to the pixmap
     used by the screen's SaveRestoreImage() function to hold the
     screen's contents while switched out.

   Other layers may wrap the ChipEnterVT() and ChipLeaveVT()
   functions if they need to take some action when these events
   are received.

End of server generation

   At the end of each server generation, the DIX layer calls
   ChipCloseScreen() for each screen:

    Bool ChipCloseScreen(int index, ScreenPtr pScreen);

     This function should restore the saved video state and unmap
     the memory regions.

     It should also free per-screen data structures allocated by
     the driver. Note that the persistent data held in the
     ScrnInfoRec's driverPrivate field should not be freed here
     because it is needed by subsequent server generations.

     The ScrnInfoRec's vtSema field should be set to FALSE once
     the video HW state has been restored.

     Before freeing the per-screen driver data the saved
     CloseScreen value should be restored to
     pScreen->CloseScreen, and that function should be called
     after freeing the data.

Optional Driver Functions

   The functions outlined here can be called from the XFree86
   common layer, but their presence is optional.

Mode Validation

   When a mode validation helper supplied by the XFree86-common
   layer is being used, it can be useful to provide a function to
   check for hw specific mode constraints:

    ModeStatus ChipValidMode(ScrnInfoPtr pScrn, DisplayModePtr mode,
                             Bool verbose, int flags);

     Check the passed mode for hw-specific constraints, and
     return the appropriate status value.

   This function may also modify the effective timings and clock
   of the passed mode. These have been stored in the mode's Crtc*
   and SynthClock elements, and have already been adjusted for
   interlacing, doublescanning, multiscanning and clock
   multipliers and dividers. The function should not modify any
   other mode field, unless it wants to modify the mode timings
   reported to the user by xf86PrintModes().

   The function is called once for every mode in the xorg.conf
   Monitor section assigned to the screen, with flags set to
   MODECHECK_INITIAL. It is subsequently called for every mode in
   the xorg.conf Display subsection assigned to the screen, with
   flags set to MODECHECK_FINAL. In the second case, the mode will
   have successfully passed all other tests. In addition, the
   ScrnInfoRec's virtualX, virtualY and displayWidth fields will
   have been set as if the mode to be validated were to be the
   last mode accepted.

   In effect, calls with MODECHECK_INITIAL are intended for checks
   that do not depend on any mode other than the one being
   validated, while calls with MODECHECK_FINAL are intended for
   checks that may involve more than one mode.

Free screen data

   When a screen is deleted prior to the completion of the
   ScreenInit phase the ChipFreeScreen() function is called when
   defined.

    void ChipFreeScreen(ScrnInfoPtr pScrn);

     Free any driver-allocated data that may have been allocated
     up to and including an unsuccessful ChipScreenInit() call.
     This would predominantly be data allocated by ChipPreInit()
     that persists across server generations. It would include
     the driverPrivate, and any “privates” entries that modules
     may have allocated.

Recommended driver functions

   The functions outlined here are for internal use by the driver
   only. They are entirely optional, and are never accessed
   directly from higher layers. The sample function declarations
   shown here are just examples. The interface (if any) used is up
   to the driver.

Save

   Save the video state. This could be called from
   ChipScreenInit() and (possibly) ChipEnterVT().

    void ChipSave(ScrnInfoPtr pScrn);

     Saves the current state. This will only be saving pre-server
     states or states before returning to the server. There is
     only one current saved state per screen and it is stored in
     private storage in the screen.

Restore

   Restore the original video state. This could be called from the
   ChipLeaveVT() and ChipCloseScreen() functions.

    void ChipRestore(ScrnInfoPtr pScrn);

     Restores the saved state from the private storage. Usually
     only used for restoring text modes.

Initialise Mode

   Initialise a video mode. This could be called from the
   ChipScreenInit(), ChipSwitchMode() and ChipEnterVT() functions.

    Bool ChipModeInit(ScrnInfoPtr pScrn, DisplayModePtr mode);

     Programs the hardware for the given video mode.

Data and Data Structures

Command line data

   Command line options are typically global, and are stored in
   global variables. These variables are read-only and are
   available to drivers via a function call interface. Most of
   these command line values are processed via helper functions to
   ensure that they are treated consistently by all drivers. The
   other means of access is provided for cases where the supplied
   helper functions might not be appropriate.

   Some of them are:

       xf86Verbose               verbosity level
       xf86Bpp                   -bpp from the command line
       xf86Depth                 -depth from the command line
       xf86Weight                -weight from the command line
       xf86Gamma                 -{r,g,b,}gamma from the command l
   ine
       xf86FlipPixels            -flippixels from the command line
       xf86ProbeOnly             -probeonly from the command line
       defaultColorVisualClass   -cc from the command line

   If we ever do allow for screen-specific command line options,
   we may need to rethink this.

   These can be accessed in a read-only manner by drivers with the
   following functions:

    int xf86GetVerbosity();

     Returns the value of xf86Verbose.

    int xf86GetDepth();

     Returns the -depth command line setting. If not set on the
     command line, -1 is returned.

    rgb xf86GetWeight();

     Returns the -weight command line setting. If not set on the
     command line, {0, 0, 0} is returned.

    Gamma xf86GetGamma();

     Returns the -gamma or -rgamma, -ggamma, -bgamma command line
     settings. If not set on the command line, {0.0, 0.0, 0.0} is
     returned.

    Bool xf86GetFlipPixels();

     Returns TRUE if -flippixels is present on the command line,
     and FALSE otherwise.

    const char *xf86GetServerName();

     Returns the name of the X server from the command line.

Data handling

   Config file data contains parts that are global, and parts that
   are Screen specific. All of it is parsed into data structures
   that neither the drivers or most other parts of the server need
   to know about.

   The global data is typically not required by drivers, and as
   such, most of it is stored in the private xf86InfoRec.

   The screen-specific data collected from the config file is
   stored in screen, device, display, monitor-specific data
   structures that are separate from the ScrnInfoRecs, with the
   appropriate elements/fields hooked into the ScrnInfoRecs as
   required. The screen config data is held in confScreenRec,
   device data in the GDevRec, monitor data in the MonRec, and
   display data in the DispRec.

   The XFree86 common layer's screen specific data (the actual
   data in use for each screen) is held in the ScrnInfoRecs. As
   has been outlined above, the ScrnInfoRecs are allocated at
   probe time, and it is the responsibility of the Drivers'
   Probe() and PreInit() functions to finish filling them in based
   on both data provided on the command line and data provided
   from the Config file. The precedence for this is:

     command line -> config file -> probed/default data

   For most things in this category there are helper functions
   that the drivers can use to ensure that the above precedence is
   consistently used.

   As well as containing screen-specific data that the XFree86
   common layer (including essential parts of the server
   infrastructure as well as helper functions) needs to access, it
   also contains some data that drivers use internally. When
   considering whether to add a new field to the ScrnInfoRec,
   consider the balance between the convenience of things that
   lots of drivers need and the size/obscurity of the ScrnInfoRec.

   Per-screen driver specific data that cannot be accommodated
   with the static ScrnInfoRec fields is held in a driver-defined
   data structure, a pointer to which is assigned to the
   ScrnInfoRec's driverPrivate field. This is per-screen data that
   persists across server generations (as does the bulk of the
   static ScrnInfoRec data). It would typically also include the
   video card's saved state.

   Per-screen data for other modules that the driver uses that is
   reset for each server generation is hooked into the ScrnInfoRec
   through its privates field.

   Once it has stabilised, the data structures and variables
   accessible to video drivers will be documented here. In the
   meantime, those things defined in the xf86.h and xf86str.h
   files are visible to video drivers. Things defined in
   xf86Priv.h and xf86Privstr.h are NOT intended to be visible to
   video drivers, and it is an error for a driver to include those
   files.

Accessing global data

   Some other global state information that the drivers may access
   via functions is as follows:

    Bool xf86ServerIsExiting();

     Returns TRUE if the server is at the end of a generation and
     is in the process of exiting, and FALSE otherwise.

    Bool xf86ServerIsResetting();

     Returns TRUE if the server is at the end of a generation and
     is in the process of resetting, and FALSE otherwise.

    Bool xf86ServerIsOnlyProbing();

     Returns TRUE if the -probeonly command line flag was
     specified, and FALSE otherwise.

    Bool xf86CaughtSignal();

     Returns TRUE if the server has caught a signal, and FALSE
     otherwise.

Allocating private data

   A driver and any module it uses may allocate per-screen private
   storage in either the ScreenRec (DIX level) or ScrnInfoRec
   (XFree86 common layer level). ScreenRec storage persists only
   for a single server generation, and ScrnInfoRec storage
   persists across generations for the lifetime of the server.

   The ScreenRec devPrivates data must be reallocated/initialised
   at the start of each new generation. This is normally done from
   the ChipScreenInit() function, and Init functions for other
   modules that it calls. Data allocated in this way should be
   freed by the driver's ChipCloseScreen() functions, and Close
   functions for other modules that it calls. A new devPrivates
   entry is allocated by calling the AllocateScreenPrivateIndex()
   function.

    int AllocateScreenPrivateIndex();

     This function allocates a new element in the devPrivates
     field of all currently existing ScreenRecs. The return value
     is the index of this new element in the devPrivates array.
     The devPrivates field is of type DevUnion:
        typedef union _DevUnion {
            pointer             ptr;
            long                val;
            unsigned long       uval;
            pointer             (*fptr)(void);
        } DevUnion;

     which allows the element to be used for any of the above
     types. It is commonly used as a pointer to data that the
     caller allocates after the new index has been allocated.

     This function will return -1 when there is an error
     allocating the new index.

   The ScrnInfoRec privates data persists for the life of the
   server, so only needs to be allocated once. This should be done
   from the ChipPreInit() function, and Init functions for other
   modules that it calls. Data allocated in this way should be
   freed by the driver's ChipFreeScreen() functions, and Free
   functions for other modules that it calls. A new privates entry
   is allocated by calling the xf86AllocateScrnInfoPrivateIndex()
   function.

    int xf86AllocateScrnInfoPrivateIndex();

     This function allocates a new element in the privates field
     of all currently existing ScrnInfoRecs. The return value is
     the index of this new element in the privates array. The
     privates field is of type DevUnion:
        typedef union _DevUnion {
            pointer             ptr;
            long                val;
            unsigned long       uval;
            pointer             (*fptr)(void);
        } DevUnion;

     which allows the element to be used for any of the above
     types. It is commonly used as a pointer to data that the
     caller allocates after the new index has been allocated.

     This function will not return when there is an error
     allocating the new index. When there is an error it will
     cause the server to exit with a fatal error. The similar
     function for allocation privates in the ScreenRec
     (AllocateScreenPrivateIndex()) differs in this respect by
     returning -1 when the allocation fails.

Keeping Track of Bus Resources

Theory of Operation

   The XFree86 common layer has knowledge of generic access
   control mechanisms for devices on certain bus systems
   (currently the PCI bus) as well as of methods to enable or
   disable access to the buses itself. Furthermore it can access
   information on resources decoded by these devices and if
   necessary modify it.

   When first starting the Xserver collects all this information,
   saves it for restoration, checks it for consistency, and if
   necessary, corrects it. Finally it disables all resources on a
   generic level prior to calling any driver function.

   When the Probe() function of each driver is called the device
   sections are matched against the devices found in the system.
   The driver may probe devices at this stage that cannot be
   identified by using device independent methods. Access to all
   resources that can be controlled in a device independent way is
   disabled. The Probe() function should register all
   non-relocatable resources at this stage. If a resource conflict
   is found between exclusive resources the driver will fail
   immediately. Optionally the driver might specify an
   EntityInit(), EntityLeave() and EntityEnter() function.

   EntityInit() can be used to disable any shared resources that
   are not controlled by the generic access control functions. It
   is called prior to the PreInit phase regardless if an entity is
   active or not. When calling the EntityInit(), EntityEnter() and
   EntityLeave() functions the common level will disable access to
   all other entities on a generic level. Since the common level
   has no knowledge of device specific methods to disable access
   to resources it cannot be guaranteed that certain resources are
   not decoded by any other entity until the EntityInit() or
   EntityEnter() phase is finished. Device drivers should
   therefore register all those resources which they are going to
   disable. If these resources are never to be used by any driver
   function they may be flagged ResInit so that they can be
   removed from the resource list after processing all
   EntityInit() functions. EntityEnter() should disable decoding
   of all resources which are not registered as exclusive and
   which are not handled by the generic access control in the
   common level. The difference to EntityInit() is that the latter
   one is only called once during lifetime of the server. It can
   therefore be used to set up variables prior to disabling
   resources. EntityLeave() should restore the original state when
   exiting the server or switching to a different VT. It also
   needs to disable device specific access functions if they need
   to be disabled on server exit or VT switch. The default state
   is to enable them before giving up the VT.

   In PreInit() phase each driver should check if any sharable
   resources it has registered during Probe() has been denied and
   take appropriate action which could simply be to fail. If it
   needs to access resources it has disabled during EntitySetup()
   it can do so provided it has registered these and will disable
   them before returning from PreInit(). This also applies to all
   other driver functions. Several functions are provided to
   request resource ranges, register these, correct PCI config
   space and add replacements for the generic access functions.
   Resources may be marked “disabled” or “unused” during OPERATING
   stage. Although these steps could also be performed in
   ScreenInit(), this is not desirable.

   Following PreInit() phase the common level determines if
   resource access control is needed. This is the case if more
   than one screen is used. If necessary the RAC wrapper module is
   loaded. In ScreenInit() the drivers can decide which operations
   need to be placed under RAC. Available are the frame buffer
   operations, the pointer operations and the colormap operations.
   Any operation that requires resources which might be disabled
   during OPERATING state should be set to use RAC. This can be
   specified separately for memory and IO resources.

   When ScreenInit() phase is done the common level will determine
   which shared resources are requested by more than one driver
   and set the access functions accordingly. This is done
   following these rules:
    1. The sharable resources registered by each entity are
       compared. If a resource is registered by more than one
       entity the entity will be marked to need to share this
       resources type (IO or MEM).
    2. A resource marked “disabled” during OPERATING state will be
       ignored entirely.
    3. A resource marked “unused” will only conflicts with an
       overlapping resource of an other entity if the second is
       actually in use during OPERATING state.
    4. If an “unused” resource was found to conflict however the
       entity does not use any other resource of this type the
       entire resource type will be disabled for that entity.

   The driver has the choice among different ways to control
   access to certain resources:
    1. It can rely on the generic access functions. This is
       probably the most common case. Here the driver only needs
       to register any resource it is going to use.
    2. It can replace the generic access functions by driver
       specific ones. This will mostly be used in cases where no
       generic access functions are available. In this case the
       driver has to make sure these resources are disabled when
       entering the PreInit() stage. Since the replacement
       functions are registered in PreInit() the driver will have
       to enable these resources itself if it needs to access them
       during this state. The driver can specify if the
       replacement functions can control memory and/or I/O
       resources separately.
    3. The driver can enable resources itself when it needs them.
       Each driver function enabling them needs to disable them
       before it will return. This should be used if a resource
       which can be controlled in a device dependent way is only
       required during SETUP state. This way it can be marked
       “unused” during OPERATING state.

   A resource which is decoded during OPERATING state however
   never accessed by the driver should be marked unused.

   Since access switching latencies are an issue during Xserver
   operation, the common level attempts to minimize the number of
   entities that need to be placed under RAC control. When a
   wrapped operation is called, the EnableAccess() function is
   called before control is passed on. EnableAccess() checks if a
   screen is under access control. If not it just establishes bus
   routing and returns. If the screen needs to be under access
   control, EnableAccess() determines which resource types (MEM,
   IO) are required. Then it tests if this access is already
   established. If so it simply returns. If not it disables the
   currently established access, fixes bus routing and enables
   access to all entities registered for this screen.

   Whenever a mode switch or a VT-switch is performed the common
   level will return to SETUP state.

Resource Types

   Resource have certain properties. When registering resources
   each range is accompanied by a flag consisting of the ORed
   flags of the different properties the resource has. Each
   resource range may be classified according to
     * its physical properties i.e., if it addresses memory
       (ResMem) or I/O space (ResIo),
     * if it addresses a block (ResBlock) or sparse (ResSparse)
       range,
     * its access properties.

   There are two known access properties:
     * ResExclusive for resources which may not be shared with any
       other device and
     * ResShared for resources which can be disabled and therefore
       can be shared.

   If it is necessary to test a resource against any type a
   generic access type ResAny is provided. If this is set the
   resource will conflict with any resource of a different entity
   intersecting its range. Further it can be specified that a
   resource is decoded however never used during any stage
   (ResUnused) or during OPERATING state (ResUnusedOpr). A
   resource only visible during the init functions (ie.
   EntityInit(), EntityEnter() and EntityLeave() should be
   registered with the flag ResInit. A resource that might
   conflict with background resource ranges may be flagged with
   ResBios. This might be useful when registering resources ranges
   that were assigned by the system Bios.

   Several predefined resource lists are available for VGA and
   8514/A resources in common/xf86Resources.h.

Available Functions

   The functions provided for resource management are listed in
   their order of use in the driver.

Probe Phase

   In this phase each driver detects those resources it is able to
   drive, creates an entity record for each of them, registers
   non-relocatable resources and allocates screens and adds the
   resources to screens.

   Two helper functions are provided for matching device sections
   in the xorg.conf file to the devices:

    int xf86MatchPciInstances(const char *driverName, int vendorID,
                              SymTabPtr chipsets, PciChipsets *PCIchipse
ts,
                              GDevPtr *devList, int numDevs, DriverPtr d
rvp,
                              int **foundEntities);

     This function finds matches between PCI cards that a driver
     supports and config file device sections. It is intended for
     use in the ChipProbe() function of drivers for PCI cards.
     Only probed PCI devices with a vendor ID matching vendorID
     are considered. devList and numDevs are typically those
     found from calling xf86MatchDevice(), and represent the
     active config file device sections relevant to the driver.
     PCIchipsets is a table that provides a mapping between the
     PCI device IDs, the driver's internal chipset tokens and a
     list of fixed resources.

     When a device section doesn't have a BusID entry it can only
     match the primary video device. Secondary devices are only
     matched with device sections that have a matching BusID
     entry.

     Once the preliminary matches have been found, a final match
     is confirmed by checking if the chipset override, ChipID
     override or probed PCI chipset type match one of those given
     in the chipsets and PCIchipsets lists. The PCIchipsets list
     includes a list of the PCI device IDs supported by the
     driver. The list should be terminated with an entry with PCI
     ID -1". The chipsets list is a table mapping the driver's
     internal chipset tokens to names, and should be terminated
     with a NULL entry. Only those entries with a corresponding
     entry in the PCIchipsets list are considered. The order of
     precedence is: config file chipset, config file ChipID,
     probed PCI device ID.

     In cases where a driver handles PCI chipsets with more than
     one vendor ID, it may set vendorID to 0, and OR each devID
     in the list with (the vendor ID << 16).

     Entity index numbers for confirmed matches are returned as
     an array via foundEntities. The PCI information, chipset
     token and device section for each match are found in the
     EntityInfoRec referenced by the indices.

     The function return value is the number of confirmed
     matches. A return value of -1 indicates an internal error.
     The returned foundEntities array should be freed by the
     driver with xfree() when it is no longer needed in cases
     where the return value is greater than zero.

    int xf86MatchIsaInstances(const char *driverName,
                              SymTabPtr chipsets, IsaChipsets *ISAchipse
ts,
                              DriverPtr drvp, FindIsaDevProc FindIsaDevi
ce,
                              GDevPtr *devList, int numDevs,
                              int **foundEntities);

     This function finds matches between ISA cards that a driver
     supports and config file device sections. It is intended for
     use in the ChipProbe() function of drivers for ISA cards.
     devList and numDevs are typically those found from calling
     xf86MatchDevice(), and represent the active config file
     device sections relevant to the driver. ISAchipsets is a
     table that provides a mapping between the driver's internal
     chipset tokens and the resource classes. FindIsaDevice is a
     driver-provided function that probes the hardware and
     returns the chipset token corresponding to what was
     detected, and -1 if nothing was detected.

     If the config file device section contains a chipset entry,
     then it is checked against the chipsets list. When no
     chipset entry is present, the FindIsaDevice function is
     called instead.

     Entity index numbers for confirmed matches are returned as
     an array via foundEntities. The chipset token and device
     section for each match are found in the EntityInfoRec
     referenced by the indices.

     The function return value is the number of confirmed
     matches. A return value of -1 indicates an internal error.
     The returned foundEntities array should be freed by the
     driver with xfree() when it is no longer needed in cases
     where the return value is greater than zero.

   These two helper functions make use of several core functions
   that are available at the driver level:

    Bool xf86ParsePciBusString(const char *busID, int *bus,
                               int *device, int *func);

     Takes a BusID string, and if it is in the correct format,
     returns the PCI bus, device, func values that it indicates.
     The format of the string is expected to be
     "PCI:bus:device:func" where each of “bus”, “device” and
     “func” are decimal integers. The ":func" part may be
     omitted, and the func value assumed to be zero, but this
     isn't encouraged. The "PCI" prefix may also be omitted. The
     prefix "AGP" is currently equivalent to the "PCI" prefix. If
     the string isn't a valid PCI BusID, the return value is
     FALSE.

    Bool xf86ComparePciBusString(const char *busID, int bus,
                                 int device, int func);

     Compares a BusID string with PCI bus, device, func values.
     If they match TRUE is returned, and FALSE if they don't.

    Bool xf86ParseIsaBusString(const char *busID);

     Compares a BusID string with the ISA bus ID string ("ISA" or
     "ISA:"). If they match TRUE is returned, and FALSE if they
     don't.

    Bool xf86CheckPciSlot(int bus, int device, int func);

     Checks if the PCI slot bus:device:func has been claimed. If
     so, it returns FALSE, and otherwise TRUE.

    int xf86ClaimPciSlot(int bus, int device, int func, DriverPtr drvp,
                         int chipset, GDevPtr dev, Bool active);

     This function is used to claim a PCI slot, allocate the
     associated entity record and initialise their data
     structures. The return value is the index of the newly
     allocated entity record, or -1 if the claim fails. This
     function should always succeed if xf86CheckPciSlot()
     returned TRUE for the same PCI slot.

    Bool xf86IsPrimaryPci(void);

     This function returns TRUE if the primary card is a PCI
     device, and FALSE otherwise.

    int xf86ClaimIsaSlot(DriverPtr drvp, int chipset,
                         GDevPtr dev, Bool active);

     This allocates an entity record entity and initialise the
     data structures. The return value is the index of the newly
     allocated entity record.

    Bool xf86IsPrimaryIsa(void);

     This function returns TRUE if the primary card is an ISA
     (non-PCI) device, and FALSE otherwise.

   Two helper functions are provided to aid configuring entities:

    ScrnInfoPtr xf86ConfigPciEntity(ScrnInfoPtr pScrn,
                                    int scrnFlag, int entityIndex,
                                    PciChipsets *p_chip,
                                    resList res, EntityProc init,
                                    EntityProc enter, EntityProc leave,
                                    pointer private);

    ScrnInfoPtr xf86ConfigIsaEntity(ScrnInfoPtr pScrn,
                                    int scrnFlag, int entityIndex,
                                    IsaChipsets *i_chip,
                                    resList res, EntityProc init,
                                    EntityProc enter, EntityProc leave,
                                    pointer private);

     These functions are used to register the non-relocatable
     resources for an entity, and the optional entity-specific
     Init, Enter and Leave functions. Usually the list of fixed
     resources is obtained from the Isa/PciChipsets lists.
     However an additional list of resources may be passed.
     Generally this is not required. For active entities a
     ScrnInfoRec is allocated if the pScrn argument is NULL. The
     return value is TRUE when successful. The init, enter, leave
     functions are defined as follows:

        typedef void (*EntityProc)(int entityIndex,
                                   pointer private);

     They are passed the entity index and a pointer to a private
     scratch area. This can be set up during Probe() and its
     address can be passed to xf86ConfigIsaEntity() and
     xf86ConfigPciEntity() as the last argument.

   These two helper functions make use of several core functions
   that are available at the driver level:

    void xf86ClaimFixedResources(resList list, int entityIndex);

     This function registers the non-relocatable resources which
     cannot be disabled and which therefore would cause the
     server to fail immediately if they were found to conflict.
     It also records non-relocatable but sharable resources for
     processing after the Probe() phase.

    Bool xf86SetEntityFuncs(int entityIndex, EntityProc init,
                            EntityProc enter, EntityProc leave, pointer)
;

     This function registers with an entity the init, enter,
     leave functions along with the pointer to their private
     area.

    void xf86AddEntityToScreen(ScrnInfoPtr pScrn, int entityIndex);

     This function associates the entity referenced by
     entityIndex with the screen.

PreInit Phase

   During this phase the remaining resources should be registered.
   PreInit() should call xf86GetEntityInfo() to obtain a pointer
   to an EntityInfoRec for each entity it is able to drive and
   check if any resource are listed in its resources field. If
   resources registered in the Probe phase have been rejected in
   the post-Probe phase (resources is non-NULL), then the driver
   should decide if it can continue without using these or if it
   should fail.

    EntityInfoPtr xf86GetEntityInfo(int entityIndex);

     This function returns a pointer to the EntityInfoRec
     referenced by entityIndex. The returned EntityInfoRec should
     be freed with xfree() when no longer needed.

   Several functions are provided to simplify resource
   registration:

    Bool xf86IsEntityPrimary(int entityIndex);

     This function returns TRUE if the entity referenced by
     entityIndex is the primary display device (i.e., the one
     initialised at boot time and used in text mode).

    Bool xf86IsScreenPrimary(ScrnInfoPtr pScrn);

     This function returns TRUE if the primary entity is
     registered with the screen referenced by pScrn.

    pciVideoPtr xf86GetPciInfoForEntity(int entityIndex);

     This function returns a pointer to the pciVideoRec for the
     specified entity. If the entity is not a PCI device, NULL is
     returned.

   The primary function for registration of resources is:

    resPtr xf86RegisterResources(int entityIndex, resList list,
                                 int access);

     This function tries to register the resources in list. If
     list is NULL it tries to determine the resources
     automatically. This only works for entities that provide a
     generic way to read out the resource ranges they decode. So
     far this is only the case for PCI devices. By default the
     PCI resources are registered as shared (ResShared) if the
     driver wants to set a different access type it can do so by
     specifying the access flags in the third argument. A value
     of 0 means to use the default settings. If for any reason
     the resource broker is not able to register some of the
     requested resources the function will return a pointer to a
     list of the failed ones. In this case the driver may be able
     to move the resource to different locations. In case of PCI
     bus entities this is done by passing the list of failed
     resources to xf86ReallocatePciResources(). When the
     registration succeeds, the return value is NULL.

    resPtr xf86ReallocatePciResources(int entityIndex, resPtr pRes);

     This function takes a list of PCI resources that need to be
     reallocated and returns NULL when all relocations are
     successful. xf86RegisterResources() should be called again
     to register the relocated resources with the broker. If the
     reallocation fails, a list of the resources that could not
     be relocated is returned.

   Two functions are provided to obtain a resource range of a
   given type:

    resRange xf86GetBlock(long type, memType size,
                          memType window_start, memType window_end,
                          memType align_mask, resPtr avoid);

     This function tries to find a block range of size size and
     type type in a window bound by window_start and window_end
     with the alignment specified in align_mask. Optionally a
     list of resource ranges which should be avoided within the
     window can be supplied. On failure a zero-length range of
     type ResEnd will be returned.

    resRange xf86GetSparse(long type, memType fixed_bits,
                           memType decode_mask, memType address_mask,
                           resPtr avoid);

     This function is like the previous one, but attempts to find
     a sparse range instead of a block range. Here three values
     have to be specified: the address_mask which marks all bits
     of the mask part of the address, the decode_mask which masks
     out the bits which are hardcoded and are therefore not
     available for relocation and the values of the fixed bits.
     The function tries to find a base that satisfies the given
     condition. If the function fails it will return a zero range
     of type ResEnd. Optionally it might be passed a list of
     resource ranges to avoid.

   Some PCI devices are broken in the sense that they return
   invalid size information for a certain resource. In this case
   the driver can supply the correct size and make sure that the
   resource range allocated for the card is large enough to hold
   the address range decoded by the card. The function
   xf86FixPciResource() can be used to do this:

    Bool xf86FixPciResource(int entityIndex, unsigned int prt,
                            CARD32 alignment, long type);

     This function fixes a PCI resource allocation. The prt
     parameter contains the number of the PCI base register that
     needs to be fixed (0-5, and 6 for the BIOS base register).
     The size is specified by the alignment. Since PCI resources
     need to span an integral range of size 2^n, the alignm ent
     also specifies the number of addresses that will be decoded.
     If the driver specifies a type mask it can override the
     default type for PCI resources which is ResShared. The
     resource broker needs to know that to find a matching
     resource range. This function should be called before
     calling xf86RegisterResources(). The return value is TRUE
     when the function succeeds.

    Bool xf86CheckPciMemBase(pciVideoPtr pPci, memType base);

     This function checks that the memory base address specified
     matches one of the PCI base address register values for the
     given PCI device. This is mostly used to check that an
     externally provided base address (e.g., from a config file)
     matches an actual value allocated to a device.

   The driver may replace the generic access control functions for
   an entity. This is done with the xf86SetAccessFuncs():

    void xf86SetAccessFuncs(EntityInfoPtr pEnt,
                            xf86SetAccessFuncPtr funcs,
                            xf86SetAccessFuncPtr oldFuncs);

     with:
      typedef struct {
          xf86AccessPtr mem;
          xf86AccessPtr io;
          xf86AccessPtr io_mem;
      } xf86SetAccessFuncRec, *xf86SetAccessFuncPtr;

     The driver can pass three functions: one for I/O access, one
     for memory access and one for combined memory and I/O
     access. If the memory access and combined access functions
     are identical the common level assumes that the memory
     access cannot be controlled independently of I/O access, if
     the I/O access function and the combined access functions
     are the same it is assumed that I/O can not be controlled
     independently. If memory and I/O have to be controlled
     together all three values should be the same. If a non NULL
     value is passed as third argument it is interpreted as an
     address where to store the old access record. If the third
     argument is NULL it will be assumed that the generic access
     should be enabled before replacing the access functions.
     Otherwise it will be disabled. The driver may enable them
     itself using the returned values. It should do this from its
     replacement access functions as the generic access may be
     disabled by the common level on certain occasions. If
     replacement functions are specified they must control all
     resources of the specific type registered for the entity.

   To find out if a specific resource range conflicts with another
   resource the xf86ChkConflict() function may be used:

    memType xf86ChkConflict(resRange *rgp, int entityIndex);

     This function checks if the resource range rgp of for the
     specified entity conflicts with with another resource. If a
     conflict is found, the address of the start of the conflict
     is returned. The return value is zero when there is no
     conflict.

   The OPERATING state properties of previously registered fixed
   resources can be set with the xf86SetOperatingState() function:

    resPtr xf86SetOperatingState(resList list, int entityIndex,
                                 int mask);

     This function is used to set the status of a resource during
     OPERATING state. list holds a list to which mask is to be
     applied. The parameter mask may have the value ResUnusedOpr
     and ResDisableOpr. The first one should be used if a
     resource isn't used by the driver during OPERATING state
     although it is decoded by the device, while the latter one
     indicates that the resource is not decoded during OPERATING
     state. Note that the resource ranges have to match those
     specified during registration. If a range has been specified
     starting at A and ending at B and suppose C us a value
     satisfying A < C < B one may not specify the resource range
     (A,B) by splitting it into two ranges (A,C) and (C,B).

   The following two functions are provided for special cases:

    void xf86RemoveEntityFromScreen(ScrnInfoPtr pScrn, int entityIndex);

     This function may be used to remove an entity from a screen.
     This only makes sense if a screen has more than one entity
     assigned or the screen is to be deleted. No test is made if
     the screen has any entities left.

    void xf86DeallocateResourcesForEntity(int entityIndex, long type);

     This function deallocates all resources of a given type
     registered for a certain entity from the resource broker
     list.

ScreenInit Phase

   All that is required in this phase is to setup the RAC flags.
   Note that it is also permissible to set these flags up in the
   PreInit phase. The RAC flags are held in the racIoFlags and
   racMemFlags fields of the ScrnInfoRec for each screen. They
   specify which graphics operations might require the use of
   shared resources. This can be specified separately for memory
   and I/O resources. The available flags are defined in
   rac/xf86RAC.h. They are:

   RAC_FB

   for framebuffer operations (including hw acceleration)

   RAC_CURSOR

   for Cursor operations (??? I'm not sure if we need this for SW
   cursor it depends on which level the sw cursor is drawn)

   RAC_COLORMAP

   for colormap operations

   RAC_VIEWPORT

   for the call to ChipAdjustFrame()

   The flags are ORed together.

Config file “Option” entries

   Option entries are permitted in most sections and subsections
   of the config file. There are two forms of option entries:

   Option "option-name"

                                      A boolean option.

   Option "option-name" "option-value"

                                      An option with an arbitrary value.

   The option entries are handled by the parser, and a list of the
   parsed options is included with each of the appropriate data
   structures that the drivers have access to. The data structures
   used to hold the option information are opaque to the driver,
   and a driver must not access the option data directly. Instead,
   the common layer provides a set of functions that may be used
   to access, check and manipulate the option data.

   First, the low level option handling functions. In most cases
   drivers would not need to use these directly.

    XF86OptionPtr xf86FindOption(XF86OptionPtr options, const char *name
);

     Takes a list of options and an option name, and returns a
     handle for the first option entry in the list matching the
     name. Returns NULL if no match is found.

    const char *xf86FindOptionValue(XF86OptionPtr options, const char *n
ame);

     Takes a list of options and an option name, and returns the
     value associated with the first option entry in the list
     matching the name. If the matching option has no value, an
     empty string ("") is returned. Returns NULL if no match is
     found.

    void xf86MarkOptionUsed(XF86OptionPtr option);

     Takes a handle for an option, and marks that option as used.

    void xf86MarkOptionUsedByName(XF86OptionPtr options, const char *nam
e);

     Takes a list of options and an option name and marks the
     first option entry in the list matching the name as used.

   Next, the higher level functions that most drivers would use.

    void xf86CollectOptions(ScrnInfoPtr pScrn, XF86OptionPtr extraOpts);

     Collect the options from each of the config file sections
     used by the screen (pScrn) and return the merged list as
     pScrn->options. This function requires that
     pScrn->confScreen, pScrn->display, pScrn->monitor,
     pScrn->numEntities, and pScrn->entityList are initialised.
     extraOpts may optionally be set to an additional list of
     options to be combined with the others. The order of
     precedence for options is extraOpts, display, confScreen,
     monitor, device.

    void xf86ProcessOptions(int scrnIndex, XF86OptionPtr options,
                            OptionInfoPtr optinfo);

     Processes a list of options according to the information in
     the array of OptionInfoRecs (optinfo). The resulting
     information is stored in the value fields of the appropriate
     optinfo entries. The found fields are set to TRUE when an
     option with a value of the correct type if found, and FALSE
     otherwise. The type field is used to determine the expected
     value type for each option. Each option in the list of
     options for which there is a name match (but not necessarily
     a value type match) is marked as used. Warning messages are
     printed when option values don't match the types specified
     in the optinfo data.

     NOTE: If this function is called before a driver's screen
     number is known (e.g., from the ChipProbe() function) a
     scrnIndex value of -1 should be used.

     NOTE 2: Given that this function stores into the
     OptionInfoRecs pointed to by optinfo, the caller should
     ensure the OptionInfoRecs are (re-)initialised before the
     call, especially if the caller expects to use the predefined
     option values as defaults.

     The OptionInfoRec is defined as follows:
      typedef struct {
          double freq;
          int units;
      } OptFrequency;

      typedef union {
          unsigned long       num;
          char *              str;
          double              realnum;
          Bool                bool;
          OptFrequency        freq;
      } ValueUnion;

      typedef enum {
          OPTV_NONE = 0,
          OPTV_INTEGER,
          OPTV_STRING,  /* a non-empty string */
          OPTV_ANYSTR,  /* Any string, including an empty one */
          OPTV_REAL,
          OPTV_BOOLEAN,
          OPTV_PERCENT,
          OPTV_FREQ
      } OptionValueType;

      typedef enum {
          OPTUNITS_HZ = 1,
          OPTUNITS_KHZ,
          OPTUNITS_MHZ
      } OptFreqUnits;

      typedef struct {
          int                 token;
          const char*         name;
          OptionValueType     type;
          ValueUnion          value;
          Bool                found;
      } OptionInfoRec, *OptionInfoPtr;

     OPTV_FREQ can be used for options values that are
     frequencies. These values are a floating point number with
     an optional unit name appended. The unit name can be one of
     "Hz", "kHz", "k", "MHz", "M". The multiplier associated with
     the unit is stored in freq.units, and the scaled frequency
     is stored in freq.freq. When no unit is specified,
     freq.units is set to 0, and freq.freq is unscaled.

     OPTV_PERCENT can be used for option values that are
     specified in percent (e.g. "20%"). These values are a
     floating point number with a percent sign appended. If the
     percent sign is missing, the parser will fail to match the
     value.

     Typical usage is to setup an array of OptionInfoRecs with
     all fields initialised. The value and found fields get set
     by xf86ProcessOptions(). For cases where the value parsing
     is more complex, the driver should specify OPTV_STRING, and
     parse the string itself. An example of using this option
     handling is included in the Sample Driver section.

    void xf86ShowUnusedOptions(int scrnIndex, XF86OptionPtr options);

     Prints out warning messages for each option in the list of
     options that isn't marked as used. This is intended to show
     options that the driver hasn't recognised. It would normally
     be called near the end of the ChipScreenInit() function, but
     only when serverGeneration == 1

    OptionInfoPtr xf86TokenToOptinfo(const OptionInfoRec *table,
                                     int token);

     Returns a pointer to the OptionInfoRec in table with a token
     field matching token. Returns NULL if no match is found.

    Bool xf86IsOptionSet(const OptionInfoRec *table, int token);

     Returns the found field of the OptionInfoRec in table with a
     token field matching token. This can be used for options of
     all types. Note that for options of type OPTV_BOOLEAN, it
     isn't sufficient to check this to determine the value of the
     option. Returns FALSE if no match is found.

    char *xf86GetOptValString(const OptionInfoRec *table, int token);

     Returns the value.str field of the OptionInfoRec in table
     with a token field matching token. Returns NULL if no match
     is found.

    Bool xf86GetOptValInteger(const OptionInfoRec *table, int token,

                                int *value);

     Returns via *value the value.num field of the OptionInfoRec
     in table with a token field matching token. *value is only
     changed when a match is found so it can be safely
     initialised with a default prior to calling this function.
     The function return value is as for xf86IsOptionSet().

    Bool xf86GetOptValULong(const OptionInfoRec *table, int token,
                            unsigned long *value);

     Like xf86GetOptValInteger(), except the value is treated as
     an unsigned long.

    Bool xf86GetOptValReal(const OptionInfoRec *table, int token,
                           double *value);

     Like xf86GetOptValInteger(), except that value.realnum is
     used.

    Bool xf86GetOptValFreq(const OptionInfoRec *table, int token,
                           OptFreqUnits expectedUnits, double *value);

     Like xf86GetOptValInteger(), except that the value.freq data
     is returned. The frequency value is scaled to the units
     indicated by expectedUnits. The scaling is exact when the
     units were specified explicitly in the option's value.
     Otherwise, the expectedUnits field is used as a hint when
     doing the scaling. In this case, values larger than 1000 are
     assumed to have be specified in the next smallest units. For
     example, if the Option value is "10000" and expectedUnits is
     OPTUNITS_MHZ, the value returned is 10.

    Bool xf86GetOptValBool(const OptionInfoRec *table, int token, Bool *
value);

     This function is used to check boolean options
     (OPTV_BOOLEAN). If the function return value is FALSE, it
     means the option wasn't set. Otherwise *value is set to the
     boolean value indicated by the option's value. No option
     value is interpreted as TRUE. Option values meaning TRUE are
     "1", "yes", "on", "true", and option values meaning FALSE
     are "0", "no", "off", "false". Option names both with the
     "no" prefix in their names, and with that prefix removed are
     also checked and handled in the obvious way. *value is not
     changed when the option isn't present. It should normally be
     set to a default value before calling this function.

    Bool xf86ReturnOptValBool(const OptionInfoRec *table, int token, Boo
l def);

     This function is used to check boolean options
     (OPTV_BOOLEAN). If the option is set, its value is returned.
     If the options is not set, the default value specified by
     def is returned. The option interpretation is the same as
     for xf86GetOptValBool().

    int xf86NameCmp(const char *s1, const char *s2);

     This function should be used when comparing strings from the
     config file with expected values. It works like strcmp(),
     but is not case sensitive and space, tab, and “_” characters
     are ignored in the comparison. The use of this function
     isn't restricted to parsing option values. It may be used
     anywhere where this functionality required.

Modules, Drivers, Include Files and Interface Issues

   NOTE: this section is incomplete.

Include files

   The following include files are typically required by video
   drivers:

     All drivers should include these:

       "xf86.h"
       "xf86_OSproc.h"
       "xf86_ansic.h"
       "xf86Resources.h"

     Wherever inb/outb (and related things) are used the
     following should be included:

       "compiler.h"

     Note: in drivers, this must be included after
     "xf86_ansic.h".

     Drivers that need to access the PCI config space need this:

       "xf86Pci.h"

     Drivers that initialise a SW cursor need this:

       "mipointer.h"

     All drivers using the mi colourmap code need this:

       "micmap.h"

     If a driver uses the vgahw module, it needs this:

       "vgaHW.h"

     Drivers supporting VGA or Hercules monochrome screens need:

       "xf1bpp.h"

     Drivers supporting VGA or EGC 16-colour screens need:

       "xf4bpp.h"

     Drivers using cfb need:
    #define PSZ 8
    #include "cfb.h"
    #undef PSZ

     Drivers supporting bpp 16, 24 or 32 with cfb need one or
     more of:

       "cfb16.h"
       "cfb24.h"
       "cfb32.h"

     If a driver uses the fb manager, it needs this:

       "xf86fbman.h"

   Non-driver modules should include "xf86_ansic.h" to get the
   correct wrapping of ANSI C/libc functions.

   All modules must NOT include any system include files, or the
   following:

       "xf86Priv.h"
       "xf86Privstr.h"
       "xf86_OSlib.h"
       "Xos.h"

   In addition, "xf86_libc.h" must not be included explicitly. It
   is included implicitly by "xf86_ansic.h".

Offscreen Memory Manager

   Management of offscreen video memory may be handled by the
   XFree86 framebuffer manager. Once the offscreen memory manager
   is running, drivers or extensions may allocate, free or resize
   areas of offscreen video memory using the following functions
   (definitions taken from xf86fbman.h):
    typedef struct _FBArea {
        ScreenPtr    pScreen;
        BoxRec       box;
        int          granularity;
        void         (*MoveAreaCallback)(struct _FBArea*, struct _FBArea
*)
        void         (*RemoveAreaCallback)(struct _FBArea*)
        DevUnion     devPrivate;
    } FBArea, *FBAreaPtr;

    typedef void (*MoveAreaCallbackProcPtr)(FBAreaPtr from, FBAreaPtr to
)
    typedef void (*RemoveAreaCallbackProcPtr)(FBAreaPtr)

    FBAreaPtr xf86AllocateOffscreenArea (
        ScreenPtr pScreen,
        int width, int height,
        int granularity,
        MoveAreaCallbackProcPtr MoveAreaCallback,
        RemoveAreaCallbackProcPtr RemoveAreaCallback,
        pointer privData
    )

    void xf86FreeOffscreenArea (FBAreaPtr area)

    Bool xf86ResizeOffscreenArea (
        FBAreaPtr area
        int w, int h
    )

   The function:
    Bool xf86FBManagerRunning(ScreenPtr pScreen);

   can be used by an extension to check if the driver has
   initialized the memory manager. The manager is not available if
   this returns FALSE and the functions above will all fail.

   xf86AllocateOffscreenArea() can be used to request a rectangle
   of dimensions width × height (in pixels) from unused offscreen
   memory. granularity specifies that the leftmost edge of the
   rectangle must lie on some multiple of granularity pixels. A
   granularity of zero means the same thing as a granularity of
   one - no alignment preference. A MoveAreaCallback can be
   provided to notify the requester when the offscreen area is
   moved. If no MoveAreaCallback is supplied then the area is
   considered to be immovable. The privData field will be stored
   in the manager's internal structure for that allocated area and
   will be returned to the requester in the FBArea passed via the
   MoveAreaCallback. An optional RemoveAreaCallback is provided.
   If the driver provides this it indicates that the area should
   be allocated with a lower priority. Such an area may be removed
   when a higher priority request (one that doesn't have a
   RemoveAreaCallback) is made. When this function is called, the
   driver will have an opportunity to do whatever cleanup it needs
   to do to deal with the loss of the area, but it must finish its
   cleanup before the function exits since the offscreen memory
   manager will free the area immediately after.

   xf86AllocateOffscreenArea() returns NULL if it was unable to
   allocate the requested area. When no longer needed, areas
   should be freed with xf86FreeOffscreenArea().

   xf86ResizeOffscreenArea() resizes an existing FBArea.
   xf86ResizeOffscreenArea() returns TRUE if the resize was
   successful. If xf86ResizeOffscreenArea() returns FALSE, the
   original FBArea is left unmodified. Resizing an area maintains
   the area's original granularity, devPrivate, and
   MoveAreaCallback. xf86ResizeOffscreenArea() has considerably
   less overhead than freeing the old area then reallocating the
   new size, so it should be used whenever possible.

   The function:
    Bool xf86QueryLargestOffscreenArea(
      ScreenPtr pScreen,
      int *width, int *height,
      int granularity,
      int preferences,
      int priority
    );

   is provided to query the width and height of the largest single
   FBArea allocatable given a particular priority. preferences can
   be one of the following to indicate whether width, height or
   area should be considered when determining which is the largest
   single FBArea available.
  FAVOR_AREA_THEN_WIDTH
  FAVOR_AREA_THEN_HEIGHT
  FAVOR_WIDTH_THEN_AREA
  FAVOR_HEIGHT_THEN_AREA

   priority is one of the following:

     PRIORITY_LOW

     Return the largest block available without stealing anyone
     else's space. This corresponds to the priority of allocating
     a FBArea when a RemoveAreaCallback is provided.

     PRIORITY_NORMAL

     Return the largest block available if it is acceptable to
     steal a lower priority area from someone. This corresponds
     to the priority of allocating a FBArea without providing a
     RemoveAreaCallback.

     PRIORITY_EXTREME

     Return the largest block available if all FBAreas that
     aren't locked down were expunged from memory first. This
     corresponds to any allocation made directly after a call to
     xf86PurgeUnlockedOffscreenAreas().

   The function:
    Bool xf86PurgeUnlockedOffscreenAreas(ScreenPtr pScreen);

   is provided as an extreme method to free up offscreen memory.
   This will remove all removable FBArea allocations.

   Initialization of the XFree86 framebuffer manager is done via
    Bool xf86InitFBManager(ScreenPtr pScreen, BoxPtr FullBox);

   FullBox represents the area of the framebuffer that the manager
   is allowed to manage. This is typically a box with a width of
   pScrn->displayWidth and a height of as many lines as can be fit
   within the total video memory, however, the driver can reserve
   areas at the extremities by passing a smaller area to the
   manager.

Colormap Handling

   A generic colormap handling layer is provided within the
   XFree86 common layer. This layer takes care of most of the
   details, and only requires a function from the driver that
   loads the hardware palette when required. To use the colormap
   layer, a driver calls the xf86HandleColormaps() function.

    Bool xf86HandleColormaps(ScreenPtr pScreen, int maxColors,
                             int sigRGBbits, LoadPaletteFuncPtr loadPale
tte,
                             SetOverscanFuncPtr setOverscan,
                             unsigned int flags);

     This function must be called after the default colormap has
     been initialised. The pScrn->gamma field must also be
     initialised, preferably by calling xf86SetGamma(). maxColors
     is the number of entries in the palette. sigRGBbits is the
     size in bits of each color component in the DAC's palette.
     loadPalette is a driver-provided function for loading a
     colormap into the hardware, and is described below.
     setOverscan is an optional function that may be provided
     when the overscan color is an index from the standard LUT
     and when it needs to be adjusted to keep it as close to
     black as possible. The setOverscan function programs the
     overscan index. It shouldn't normally be used for depths
     other than 8. setOverscan should be set to NULL when it
     isn't needed. flags may be set to the following (which may
     be ORed together):

   CMAP_PALETTED_TRUECOLOR

   the TrueColor visual is paletted and is just a special case of
   DirectColor. This flag is only valid for bpp > 8.

   CMAP_RELOAD_ON_MODE_SWITCH

   reload the colormap automatically after mode switches. This is
   useful for when the driver is resetting the hardware during
   mode switches and corrupting or erasing the hardware palette.

   CMAP_LOAD_EVEN_IF_OFFSCREEN

   reload the colormap even if the screen is switched out of the
   server's VC. The palette is not reloaded when the screen is
   switched back in, nor after mode switches. This is useful when
   the driver needs to keep track of palette changes.

     The colormap layer normally reloads the palette after VT
     enters so it is not necessary for the driver to save and
     restore the palette when switching VTs. The driver must,
     however, still save the initial palette during server start
     up and restore it during server exit.

    void LoadPalette(ScrnInfoPtr pScrn, int numColors, int *indices,
                     LOCO *colors, VisualPtr pVisual);

     LoadPalette() is a driver-provided function for loading a
     colormap into hardware. colors is the array of RGB values
     that represent the full colormap. indices is a list of index
     values into the colors array. These indices indicate the
     entries that need to be updated. numColors is the number of
     the indices to be updated.

    void SetOverscan(ScrnInfoPtr pScrn, int overscan);

     SetOverscan() is a driver-provided function for programming
     the overscan index. As described above, it is normally only
     appropriate for LUT modes where all colormap entries are
     available for the display, but where one of them is also
     used for the overscan (typically 8bpp for VGA compatible
     LUTs). It isn't required in cases where the overscan area is
     never visible.

DPMS Extension

   Support code for the DPMS extension is included in the XFree86
   common layer. This code provides an interface between the main
   extension code, and a means for drivers to initialise DPMS when
   they support it. One function is available to drivers to do
   this initialisation, and it is always available, even when the
   DPMS extension is not supported by the core server (in which
   case it returns a failure result).

    Bool xf86DPMSInit(ScreenPtr pScreen, DPMSSetProcPtr set, int flags);

     This function registers a driver's DPMS level programming
     function set. It also checks pScrn->options for the "dpms"
     option, and when present marks DPMS as being enabled for
     that screen. The set function is called whenever the DPMS
     level changes, and is used to program the requested level.
     flags is currently not used, and should be 0. If the
     initialisation fails for any reason, including when there is
     no DPMS support in the core server, the function returns
     FALSE.

   Drivers that implement DPMS support must provide the following
   function, that gets called when the DPMS level is changed:

    void ChipDPMSSet(ScrnInfoPtr pScrn, int level, int flags);

     Program the DPMS level specified by level. Valid values of
     level are DPMSModeOn, DPMSModeStandby, DPMSModeSuspend,
     DPMSModeOff. These values are defined in
     "extensions/dpms.h".

DGA Extension

   Drivers can support the XFree86 Direct Graphics Architecture
   (DGA) by filling out a structure of function pointers and a
   list of modes and passing them to DGAInit.

    Bool DGAInit(ScreenPtr pScreen, DGAFunctionPtr funcs,
                 DGAModePtr modes, int num);

/** The DGAModeRec **/

typedef struct {
  int num;
  DisplayModePtr mode;
  int flags;
  int imageWidth;
  int imageHeight;
  int pixmapWidth;
  int pixmapHeight;
  int bytesPerScanline;
  int byteOrder;
  int depth;
  int bitsPerPixel;
  unsigned long red_mask;
  unsigned long green_mask;
  unsigned long blue_mask;
  int viewportWidth;
  int viewportHeight;
  int xViewportStep;
  int yViewportStep;
  int maxViewportX;
  int maxViewportY;
  int viewportFlags;
  int offset;
  unsigned char *address;
  int reserved1;
  int reserved2;
} DGAModeRec, *DGAModePtr;

   num

   Can be ignored. The DGA DDX will assign these numbers.

   mode

   A pointer to the DisplayModeRec for this mode.

   flags

   The following flags are defined and may be OR'd together:

   DGA_CONCURRENT_ACCESS

   Indicates that the driver supports concurrent graphics
   accelerator and linear framebuffer access.

   DGA_FILL_RECT DGA_BLIT_RECT DGA_BLIT_RECT_TRANS

   Indicates that the driver supports the FillRect, BlitRect or
   BlitTransRect functions in this mode.

   DGA_PIXMAP_AVAILABLE

   Indicates that Xlib may be used on the framebuffer. This flag
   will usually be set unless the driver wishes to prohibit this
   for some reason.

   DGA_INTERLACED DGA_DOUBLESCAN

   Indicates that these are interlaced or double scan modes.

   imageWidth imageHeight

   These are the dimensions of the linear framebuffer accessible
   by the client.

   pixmapWidth pixmapHeight

   These are the dimensions of the area of the framebuffer
   accessible by the graphics accelerator.

   bytesPerScanline

   Pitch of the framebuffer in bytes.

   byteOrder

   Usually the same as pScrn->imageByteOrder.

   depth

   The depth of the framebuffer in this mode.

   bitsPerPixel

   The number of bits per pixel in this mode.

   red_mask, green_mask, blue_mask

   The RGB masks for this mode, if applicable.

   viewportWidth, viewportHeight

   Dimensions of the visible part of the framebuffer. Usually
   mode->HDisplay and mode->VDisplay.

   xViewportStep yViewportStep

   The granularity of x and y viewport positions that the driver
   supports in this mode.

   maxViewportX maxViewportY

   The maximum viewport position supported by the driver in this
   mode.

   viewportFlags

   The following may be OR'd together:

   DGA_FLIP_IMMEDIATE

                     The driver supports immediate viewport changes.

   DGA_FLIP_RETRACE

                     The driver supports viewport changes at retrace.

   offset

   The offset into the linear framebuffer that corresponds to
   pixel (0,0) for this mode.

   address

   The virtual address of the framebuffer as mapped by the driver.
   This is needed when DGA_PIXMAP_AVAILABLE is set.

/** The DGAFunctionRec **/

typedef struct {
  Bool (*OpenFramebuffer)(
       ScrnInfoPtr pScrn,
       char **name,
       unsigned char **mem,
       int *size,
       int *offset,
       int *extra
  );
  void (*CloseFramebuffer)(ScrnInfoPtr pScrn);
  Bool (*SetMode)(ScrnInfoPtr pScrn, DGAModePtr pMode);
  void (*SetViewport)(ScrnInfoPtr pScrn, int x, int y, int flags);
  int  (*GetViewport)(ScrnInfoPtr pScrn);
  void (*Sync)(ScrnInfoPtr);
  void (*FillRect)(
       ScrnInfoPtr pScrn,
       int x, int y, int w, int h,
       unsigned long color
  );
  void (*BlitRect)(
       ScrnInfoPtr pScrn,
       int srcx, int srcy,
       int w, int h,
       int dstx, int dsty
  );
  void (*BlitTransRect)(
       ScrnInfoPtr pScrn,
       int srcx, int srcy,
       int w, int h,
       int dstx, int dsty,
       unsigned long color
  );
} DGAFunctionRec, *DGAFunctionPtr;

    Bool OpenFramebuffer (pScrn, name, mem, size, offset, extra);

     OpenFramebuffer() should pass the client everything it needs
     to know to be able to open the framebuffer. These parameters
     are OS specific and their meanings are to be interpreted by
     an OS specific client library.

   name

         The name of the device to open or NULL if there is no special
         device to open. A NULL name tells the client that it should
         open whatever device one would usually open to access physical
         memory.

   mem

         The physical address of the start of the framebuffer.

   size

         The size of the framebuffer in bytes.

   offset

         Any offset into the device, if applicable.

   flags

         Any additional information that the client may need. Currently,
         only the DGA_NEED_ROOT flag is defined.

    void CloseFramebuffer (pScrn);

     CloseFramebuffer() merely informs the driver (if it even
     cares) that client no longer needs to access the framebuffer
     directly. This function is optional.

    Bool SetMode (pScrn, pMode);

     SetMode() tells the driver to initialize the mode passed to
     it. If pMode is NULL, then the driver should restore the
     original pre-DGA mode.

    void SetViewport (pScrn, x, y, flags);

     SetViewport() tells the driver to make the upper left-hand
     corner of the visible screen correspond to coordinate (x,y)
     on the framebuffer. flags currently defined are:

   DGA_FLIP_IMMEDIATE

   The viewport change should occur immediately.

   DGA_FLIP_RETRACE

   The viewport change should occur at the vertical retrace, but
   this function should return sooner if possible.

     The (x,y) locations will be passed as the client specified
     them, however, the driver is expected to round these
     locations down to the next supported location as specified
     by the xViewportStep and yViewportStep for the current mode.

    int GetViewport (pScrn);

     GetViewport() gets the current page flip status. Set bits in
     the returned int correspond to viewport change requests
     still pending. For instance, set bit zero if the last
     SetViewport request is still pending, bit one if the one
     before that is still pending, etc.

    void Sync (pScrn);

     This function should ensure that any graphics accelerator
     operations have finished. This function should not return
     until the graphics accelerator is idle.

    void FillRect (pScrn, x, y, w, h, color);

     This optional function should fill a rectangle w × h located
     at (x,y) in the given color.

    void BlitRect (pScrn, srcx, srcy, w, h, dstx, dsty);

     This optional function should copy an area w × h located at
     (srcx,srcy) to location (dstx,dsty). This function will need
     to handle copy directions as appropriate.

    void BlitTransRect (pScrn, srcx, srcy, w, h, dstx, dsty, color);

     This optional function is the same as BlitRect except that
     pixels in the source corresponding to the color key color
     should be skipped.

The XFree86 X Video Extension (Xv) Device Dependent Layer

   XFree86 offers the X Video Extension which allows clients to
   treat video as any another primitive and “Put” video into
   drawables. By default, the extension reports no video adaptors
   as being available since the DDX layer has not been
   initialized. The driver can initialize the DDX layer by filling
   out one or more XF86VideoAdaptorRecs as described later in this
   document and passing a list of XF86VideoAdaptorPtr pointers to
   the following function:
    Bool xf86XVScreenInit(ScreenPtr pScreen,
                          XF86VideoAdaptorPtr *adaptPtrs,
                          int num);

   After doing this, the extension will report video adaptors as
   being available, providing the data in their respective
   XF86VideoAdaptorRecs was valid. xf86XVScreenInit() copies data
   from the structure passed to it so the driver may free it after
   the initialization. At the moment, the DDX only supports
   rendering into Window drawables. Pixmap rendering will be
   supported after a sufficient survey of suitable hardware is
   completed.

   The XF86VideoAdaptorRec:
typedef struct {
        unsigned int type;
        int flags;
        char *name;
        int nEncodings;
        XF86VideoEncodingPtr pEncodings;
        int nFormats;
        XF86VideoFormatPtr pFormats;
        int nPorts;
        DevUnion *pPortPrivates;
        int nAttributes;
        XF86AttributePtr pAttributes;
        int nImages;
        XF86ImagePtr pImages;
        PutVideoFuncPtr PutVideo;
        PutStillFuncPtr PutStill;
        GetVideoFuncPtr GetVideo;
        GetStillFuncPtr GetStill;
        StopVideoFuncPtr StopVideo;
        SetPortAttributeFuncPtr SetPortAttribute;
        GetPortAttributeFuncPtr GetPortAttribute;
        QueryBestSizeFuncPtr QueryBestSize;
        PutImageFuncPtr PutImage;
        QueryImageAttributesFuncPtr QueryImageAttributes;
} XF86VideoAdaptorRec, *XF86VideoAdaptorPtr;

   Each adaptor will have its own XF86VideoAdaptorRec. The fields
   are as follows:

   type

   This can be any of the following flags OR'd together.

   XvInputMask XvOutputMask

   These refer to the target drawable and are similar to a
   Window's class. XvInputMask indicates that the adaptor can put
   video into a drawable. XvOutputMask indicates that the adaptor
   can get video from a drawable.

   XvVideoMask XvStillMask XvImageMask

   These indicate that the adaptor supports video, still or image
   primitives respectively.

   XvWindowMask XvPixmapMask

   These indicate the types of drawables the adaptor is capable of
   rendering into. At the moment, Pixmap rendering is not
   supported and the XvPixmapMask flag is ignored.

   flags

   Currently, the following flags are defined:

   VIDEO_OVERLAID_STILLS

   Implementing PutStill for hardware that does video as an
   overlay can be awkward since it's unclear how long to leave the
   video up for. When this flag is set, StopVideo will be called
   whenever the destination gets clipped or moved so that the
   still can be left up until then.

   VIDEO_OVERLAID_IMAGES

   Same as VIDEO_OVERLAID_STILLS but for images.

   VIDEO_CLIP_TO_VIEWPORT

   Indicates that the clip region passed to the driver functions
   should be clipped to the visible portion of the screen in the
   case where the viewport is smaller than the virtual desktop.

   name

   The name of the adaptor.

   nEncodings pEncodings

   The number of encodings the adaptor is capable of and pointer
   to the XF86VideoEncodingRec array. The XF86VideoEncodingRec is
   described later on. For drivers that only support XvImages
   there should be an encoding named "XV_IMAGE" and the width and
   height should specify the maximum size source image supported.

   nFormats pFormats

   The number of formats the adaptor is capable of and pointer to
   the XF86VideoFormatRec array. The XF86VideoFormatRec is
   described later on.

   nPorts pPortPrivates

   The number of ports is the number of separate data streams
   which the adaptor can handle simultaneously. If you have more
   than one port, the adaptor is expected to be able to render
   into more than one window at a time. pPortPrivates is an array
   of pointers or ints - one for each port. A port's private data
   will be passed to the driver any time the port is requested to
   do something like put the video or stop the video. In the case
   where there may be many ports, this enables the driver to know
   which port the request is intended for. Most commonly, this
   will contain a pointer to the data structure containing
   information about the port. In Xv, all ports on a particular
   adaptor are expected to be identical in their functionality.

   nAttributes pAttributes

   The number of attributes recognized by the adaptor and a
   pointer to the array of XF86AttributeRecs. The XF86AttributeRec
   is described later on.

   nImages pImages

   The number of XF86ImageRecs supported by the adaptor and a
   pointer to the array of XF86ImageRecs. The XF86ImageRec is
   described later on.

   PutVideo PutStill GetVideo GetStill StopVideo SetPortAttribute
   GetPortAttribute QueryBestSize PutImage QueryImageAttributes

   These functions define the DDX->driver interface. In each case,
   the pointer data is passed to the driver. This is the port
   private for that port as described above. All fields are
   required except under the following conditions:
    1. PutVideo, PutStill and the image routines PutImage and
       QueryImageAttributes are not required when the adaptor type
       does not contain XvInputMask.
    2. GetVideo and GetStill are not required when the adaptor
       type does not contain XvOutputMask.
    3. GetVideo and PutVideo are not required when the adaptor
       type does not contain XvVideoMask.
    4. GetStill and PutStill are not required when the adaptor
       type does not contain XvStillMask.
    5. PutImage and QueryImageAttributes are not required when the
       adaptor type does not contain XvImageMask.

   With the exception of QueryImageAttributes, these functions
   should return Success if the operation was completed
   successfully. They can return XvBadAlloc otherwise.
   QueryImageAttributes returns the size of the XvImage queried.

   ClipBoxes is an X-Y banded region identical to those used
   throughout the server. The clipBoxes represent the visible
   portions of the area determined by drw_x, drw_y, drw_w and
   drw_h in the Get/Put function. The boxes are in screen
   coordinates, are guaranteed not to overlap and an empty region
   will never be passed.

    typedef  int (* PutVideoFuncPtr)( ScrnInfoPtr pScrn,
                   short vid_x, short vid_y, short drw_x, short drw_y,
                   short vid_w, short vid_h, short drw_w, short drw_h,
                   RegionPtr clipBoxes, pointer data );

     This indicates that the driver should take a subsection
     vid_w by vid_h at location (vid_x,vid_y) from the video
     stream and direct it into the rectangle drw_w by drw_h at
     location (drw_x,drw_y) on the screen, scaling as necessary.
     Due to the large variations in capabilities of the various
     hardware expected to be used with this extension, it is not
     expected that all hardware will be able to do this exactly
     as described. In that case the driver should just do “the
     best it can,” scaling as closely to the target rectangle as
     it can without rendering outside of it. In the worst case,
     the driver can opt to just not turn on the video.

    typedef  int (* PutStillFuncPtr)( ScrnInfoPtr pScrn,
                   short vid_x, short vid_y, short drw_x, short drw_y,
                   short vid_w, short vid_h, short drw_w, short drw_h,
                   RegionPtr clipBoxes, pointer data );

     This is same as PutVideo except that the driver should place
     only one frame from the stream on the screen.

    typedef int (* GetVideoFuncPtr)( ScrnInfoPtr pScrn,
                  short vid_x, short vid_y, short drw_x, short drw_y,
                  short vid_w, short vid_h, short drw_w, short drw_h,
                  RegionPtr clipBoxes, pointer data );

     This is same as PutVideo except that the driver gets video
     from the screen and outputs it. The driver should do the
     best it can to get the requested dimensions correct without
     reading from an area larger than requested.

    typedef int (* GetStillFuncPtr)( ScrnInfoPtr pScrn,
                  short vid_x, short vid_y, short drw_x, short drw_y,
                  short vid_w, short vid_h, short drw_w, short drw_h,
                  RegionPtr clipBoxes, pointer data );

     This is the same as GetVideo except that the driver should
     place only one frame from the screen into the output stream.

    typedef void (* StopVideoFuncPtr)(ScrnInfoPtr pScrn,
                                      pointer data, Bool cleanup);

     This indicates the driver should stop displaying the video.
     This is used to stop both input and output video. The
     cleanup field indicates that the video is being stopped
     because the client requested it to stop or because the
     server is exiting the current VT. In that case the driver
     should deallocate any offscreen memory areas (if there are
     any) being used to put the video to the screen. If cleanup
     is not set, the video is being stopped temporarily due to
     clipping or moving of the window, etc... and video will
     likely be restarted soon so the driver should not deallocate
     any offscreen areas associated with that port.

    typedef int (* SetPortAttributeFuncPtr)(ScrnInfoPtr pScrn,
                                Atom attribute,INT32 value, pointer data
);

    typedef int (* GetPortAttributeFuncPtr)(ScrnInfoPtr pScrn,
                                Atom attribute,INT32 *value, pointer dat
a);

     A port may have particular attributes such as hue,
     saturation, brightness or contrast. Xv clients set and get
     these attribute values by sending attribute strings (Atoms)
     to the server. Such requests end up at these driver
     functions. It is recommended that the driver provide at
     least the following attributes mentioned in the Xv client
     library docs:

   XV_ENCODING
   XV_HUE
   XV_SATURATION
   XV_BRIGHTNESS
   XV_CONTRAST

     but the driver may recognize as many atoms as it wishes. If
     a requested attribute is unknown by the driver it should
     return BadMatch. XV_ENCODING is the attribute intended to
     let the client specify which video encoding the particular
     port should be using (see the description of
     XF86VideoEncodingRec below). If the requested encoding is
     unsupported, the driver should return XvBadEncoding. If the
     value lies outside the advertised range BadValue may be
     returned. Success should be returned otherwise.

    typedef void (* QueryBestSizeFuncPtr)(ScrnInfoPtr pScrn,
                   Bool motion, short vid_w, short vid_h,
                   short drw_w, short drw_h,
                   unsigned int *p_w, unsigned int *p_h, pointer data);

     QueryBestSize provides the client with a way to query what
     the destination dimensions would end up being if they were
     to request that an area vid_w by vid_h from the video stream
     be scaled to rectangle of drw_w by drw_h on the screen.
     Since it is not expected that all hardware will be able to
     get the target dimensions exactly, it is important that the
     driver provide this function.

    typedef  int (* PutImageFuncPtr)( ScrnInfoPtr pScrn,
                   short src_x, short src_y, short drw_x, short drw_y,
                   short src_w, short src_h, short drw_w, short drw_h,
                   int image, char *buf, short width, short height,
                   Bool sync, RegionPtr clipBoxes, pointer data );

     This is similar to PutStill except that the source of the
     video is not a port but the data stored in a system memory
     buffer at buf. The data is in the format indicated by the
     image descriptor and represents a source of size width by
     height. If sync is TRUE the driver should not return from
     this function until it is through reading the data from buf.
     Returning when sync is TRUE indicates that it is safe for
     the data at buf to be replaced, freed, or modified.

    typedef  int (* QueryImageAttributesFuncPtr)( ScrnInfoPtr pScrn,
                                int image, short *width, short *height,
                                int *pitches, int *offsets);

     This function is called to let the driver specify how data
     for a particular image of size width by height should be
     stored. Sometimes only the size and corrected width and
     height are needed. In that case pitches and offsets are
     NULL. The size of the memory required for the image is
     returned by this function. The width and height of the
     requested image can be altered by the driver to reflect
     format limitations (such as component sampling periods that
     are larger than one). If pitches and offsets are not NULL,
     these will be arrays with as many elements in them as there
     are planes in the image format. The driver should specify
     the pitch (in bytes) of each scanline in the particular
     plane as well as the offset to that plane (in bytes) from
     the beginning of the image.

   The XF86VideoEncodingRec:

typedef struct {
        int id;
        char *name;
        unsigned short width, height;
        XvRationalRec rate;
} XF86VideoEncodingRec, *XF86VideoEncodingPtr;


     The XF86VideoEncodingRec specifies what encodings the
     adaptor can support. Most of this data is just informational
     and for the client's benefit, and is what will be reported
     by XvQueryEncodings. The id field is expected to be a unique
     identifier to allow the client to request a certain encoding
     via the XV_ENCODING attribute string.

   The XF86VideoFormatRec:

typedef struct {
        char  depth;
        short class;
} XF86VideoFormatRec, *XF86VideoFormatPtr;


     This specifies what visuals the video is viewable in. depth
     is the depth of the visual (not bpp). class is the visual
     class such as TrueColor, DirectColor or PseudoColor.
     Initialization of an adaptor will fail if none of the
     visuals on that screen are supported.

   The XF86AttributeRec:

typedef struct {
        int   flags;
        int   min_value;
        int   max_value;
        char  *name;
} XF86AttributeListRec, *XF86AttributeListPtr;


     Each adaptor may have an array of these advertising the
     attributes for its ports. Currently defined flags are
     XvGettable and XvSettable which may be OR'd together
     indicating that attribute is “gettable” or “settable” by the
     client. The min and max field specify the valid range for
     the value. Name is a text string describing the attribute by
     name.

   The XF86ImageRec:

typedef struct {
        int id;
        int type;
        int byte_order;
        char guid[16];
        int bits_per_pixel;
        int format;
        int num_planes;

        /* for RGB formats */
        int depth;
        unsigned int red_mask;
        unsigned int green_mask;
        unsigned int blue_mask;

        /* for YUV formats */
        unsigned int y_sample_bits;
        unsigned int u_sample_bits;
        unsigned int v_sample_bits;
        unsigned int horz_y_period;
        unsigned int horz_u_period;
        unsigned int horz_v_period;
        unsigned int vert_y_period;
        unsigned int vert_u_period;
        unsigned int vert_v_period;
        char component_order[32];
        int scanline_order;
} XF86ImageRec, *XF86ImagePtr;


     XF86ImageRec describes how video source data is laid out in
     memory. The fields are as follows:

   id

   This is a unique descriptor for the format. It is often good to
   set this value to the FOURCC for the format when applicable.

   type

   This is XvRGB or XvYUV.

   byte_order

   This is LSBFirst or MSBFirst.

   guid

   This is the Globally Unique IDentifier for the format. When not
   applicable, all characters should be NULL.

   bits_per_pixel

   The number of bits taken up (but not necessarily used) by each
   pixel. Note that for some planar formats which have fractional
   bits per pixel (such as IF09) this number may be rounded
   _down_.

   format

   This is XvPlanar or XvPacked.

   num_planes

   The number of planes in planar formats. This should be set to
   one for packed formats.

   depth

   The significant bits per pixel in RGB formats (analgous to the
   depth of a pixmap format).

   red_mask, green_mask, blue_mask

   The red, green and blue bitmasks for packed RGB formats.

   y_sample_bits, u_sample_bits, v_sample_bits

   The y, u and v sample sizes (in bits).

   horz_y_period, horz_u_period, horz_v_period

   The y, u and v sampling periods in the horizontal direction.

   vert_y_period, vert_u_period, vert_v_period

   The y, u and v sampling periods in the vertical direction.

   component_order

   Uppercase ascii characters representing the order that samples
   are stored within packed formats. For planar formats this
   represents the ordering of the planes. Unused characters in the
   32 byte string should be set to NULL.

   scanline_order

   This is XvTopToBottom or XvBottomToTop.

     Since some formats (particular some planar YUV formats) may
     not be completely defined by the parameters above, the guid,
     when available, should provide the most accurate description
     of the format.

The Loader

   This section describes the interfaces to the module loader. The
   loader interfaces can be divided into two groups: those that
   are only available to the XFree86 common layer, and those that
   are also available to modules.

Loader Overview

   The loader is capable of loading modules in a range of object
   formats, and knowledge of these formats is built in to the
   loader. Knowledge of new object formats can be added to the
   loader in a straightforward manner. This makes it possible to
   provide OS-independent modules (for a given CPU architecture
   type). In addition to this, the loader can load modules via the
   OS-provided dlopen(3) service where available. Such modules are
   not platform independent, and the semantics of dlopen() on most
   systems results in significant limitations in the use of
   modules of this type. Support for dlopen() modules in the
   loader is primarily for experimental and development purposes.

   Symbols exported by the loader (on behalf of the core X server)
   to modules are determined at compile time. Only those symbols
   explicitly exported are available to modules. All external
   symbols of loaded modules are exported to other modules, and to
   the core X server. The loader can be requested to check for
   unresolved symbols at any time, and the action to be taken for
   unresolved symbols can be controlled by the caller of the
   loader. Typically the caller identifies which symbols can
   safely remain unresolved and which cannot.

   NOTE: Now that ISO-C allows pointers to functions and pointers
   to data to have different internal representations, some of the
   following interfaces will need to be revisited.

Semi-private Loader Interface

   The following is the semi-private loader interface that is
   available to the XFree86 common layer.

    void LoaderInit(void);

     The LoaderInit() function initialises the loader, and it
     must be called once before calling any other loader
     functions. This function initialises the tables of exported
     symbols, and anything else that might need to be
     initialised.

    void LoaderSetPath(const char *path);

     The LoaderSetPath() function initialises a default module
     search path. This must be called if calls to other functions
     are to be made without explicitly specifying a module search
     path. The search path path must be a string of one or more
     comma separated absolute paths. Modules are expected to be
     located below these paths, possibly in subdirectories of
     these paths.

    pointer LoadModule(const char *module, const char *path,
                       const char **subdirlist, const char **patternlist
,
                       pointer options, const XF86ModReqInfo * modreq,
                       int *errmaj, int *errmin);

     The LoadModule() function loads the module called module.
     The return value is a module handle, and may be used in
     future calls to the loader that require a reference to a
     loaded module. The module name module is normally the
     module's canonical name, which doesn't contain any directory
     path information, or any object/library file prefixes of
     suffixes. Currently a full pathname and/or filename is also
     accepted. This might change. The other parameters are:

   path

   An optional comma-separated list of module search paths. When
   NULL, the default search path is used.

   subdirlist

   An optional NULL terminated list of subdirectories to search.
   When NULL, the default built-in list is used (refer to
   stdSubdirs in loadmod.c). The default list is also substituted
   for entries in subdirlist with the value DEFAULT_LIST. This
   makes is possible to augment the default list instead of
   replacing it. Subdir elements must be relative, and must not
   contain "..". If any violate this requirement, the load fails.

   patternlist

   An optional NULL terminated list of POSIX regular expressions
   used to connect module filenames with canonical module names.
   Each regex should contain exactly one subexpression that
   corresponds to the canonical module name. When NULL, the
   default built-in list is used (refer to stdPatterns in
   loadmod.c). The default list is also substituted for entries in
   patternlist with the value DEFAULT_LIST. This makes it possible
   to augment the default list instead of replacing it.

   options

   An optional parameter that is passed to the newly loaded
   module's SetupProc function (if it has one). This argument is
   normally a NULL terminated list of Options, and must be
   interpreted that way by modules loaded directly by the XFree86
   common layer. However, it may be used for application-specific
   parameter passing in other situations.

   modreq

   An optional XF86ModReqInfo* containing version/ABI/vendor
   information to requirements to check the newly loaded module
   against. The main purpose of this is to allow the loader to
   verify that a module of the correct type/version before running
   its SetupProc function.

   The XF86ModReqInfo struct is defined as follows:
typedef struct {
        CARD8        majorversion;  /* MAJOR_UNSPEC */
        CARD8        minorversion;  /* MINOR_UNSPEC */
        CARD16       patchlevel;    /* PATCH_UNSPEC */
        const char * abiclass;      /* ABI_CLASS_NONE */
        CARD32       abiversion;    /* ABI_VERS_UNSPEC */
        const char * moduleclass;   /* MOD_CLASS_NONE */
} XF86ModReqInfo;

   The information here is compared against the equivalent
   information in the module's XF86ModuleVersionInfo record (which
   is described below). The values in comments above indicate
   “don't care” settings for each of the fields. The comparisons
   made are as follows:

   majorversion

   Must match the module's majorversion exactly.

   minorversion

   The module's minor version must be no less than this value.
   This comparison is only made if majorversion is specified and
   matches.

   patchlevel

   The module's patchlevel must be no less than this value. This
   comparison is only made if minorversion is specified and
   matches.

   abiclass

   String must match the module's abiclass string.

   abiversion

   Must be consistent with the module's abiversion (major equal,
   minor no older).

   moduleclass

   String must match the module's moduleclass string.

   errmaj

   An optional pointer to a variable holding the major part or the
   error code. When provided, *errmaj is filled in when
   LoadModule() fails.

   errmin

   Like errmaj, but for the minor part of the error code.

    void UnloadModule(pointer mod);

     This function unloads the module referred to by the handle
     mod. All child modules are also unloaded recursively. This
     function must not be used to directly unload modules that
     are child modules (i.e., those that have been loaded with
     the LoadSubModule() described below).

Module Requirements

   Modules must provide information about themselves to the
   loader, and may optionally provide entry points for "setup" and
   "teardown" functions (those two functions are referred to here
   as SetupProc and TearDownProc).

   The module information is contained in the
   XF86ModuleVersionInfo struct, which is defined as follows:
typedef struct {
    const char * modname;      /* name of module, e.g. "foo" */
    const char * vendor;       /* vendor specific string */
    CARD32       _modinfo1_;   /* constant MODINFOSTRING1/2 to find */
    CARD32       _modinfo2_;   /* infoarea with a binary editor/sign too
l */
    CARD32       xf86version;  /* contains XF86_VERSION_CURRENT */
    CARD8        majorversion; /* module-specific major version */
    CARD8        minorversion; /* module-specific minor version */
    CARD16       patchlevel;   /* module-specific patch level */
    const char * abiclass;     /* ABI class that the module uses */
    CARD32       abiversion;   /* ABI version */
    const char * moduleclass;  /* module class */
    CARD32       checksum[4];  /* contains a digital signature of the */
                               /* version info structure */
} XF86ModuleVersionInfo;

   The fields are used as follows:

   modname

   The module's name. This field is currently only for
   informational purposes, but the loader may be modified in
   future to require it to match the module's canonical name.

   vendor

   The module vendor. This field is for informational purposes
   only.

   _modinfo1_

   This field holds the first part of a signature that can be used
   to locate this structure in the binary. It should always be
   initialised to MODINFOSTRING1.

   _modinfo2_

   This field holds the second part of a signature that can be
   used to locate this structure in the binary. It should always
   be initialised to MODINFOSTRING2.

   xf86version

   The XFree86 version against which the module was compiled. This
   is mostly for informational/diagnostic purposes. It should be
   initialised to XF86_VERSION_CURRENT, which is defined in
   xf86Version.h.

   majorversion

   The module-specific major version. For modules where this
   version is used for more than simply informational purposes,
   the major version should only change (be incremented) when ABI
   incompatibilities are introduced, or ABI components are
   removed.

   minorversion

   The module-specific minor version. For modules where this
   version is used for more than simply informational purposes,
   the minor version should only change (be incremented) when ABI
   additions are made in a backward compatible way. It should be
   reset to zero when the major version is increased.

   patchlevel

   The module-specific patch level. The patch level should
   increase with new revisions of the module where there are no
   ABI changes, and it should be reset to zero when the minor
   version is increased.

   abiclass

   The ABI class that the module requires. The class is specified
   as a string for easy extensibility. It should indicate which
   (if any) of the X server's built-in ABI classes that the module
   relies on, or a third-party ABI if appropriate. Built-in ABI
   classes currently defined are:

   ABI_CLASS_NONE

                      no class

   ABI_CLASS_ANSIC

                      only requires the ANSI C interfaces

   ABI_CLASS_VIDEODRV

                      requires the video driver ABI

   ABI_CLASS_XINPUT

                      requires the XInput driver ABI

   ABI_CLASS_EXTENSION

                      requires the extension module ABI

   abiversion

   The version of abiclass that the module requires. The version
   consists of major and minor components. The major version must
   match and the minor version must be no newer than that provided
   by the server or parent module. Version identifiers for the
   built-in classes currently defined are:

                      ABI_ANSIC_VERSION
                      ABI_VIDEODRV_VERSION
                      ABI_XINPUT_VERSION
                      ABI_EXTENSION_VERSION

   moduleclass

   This is similar to the abiclass field, except that it defines
   the type of module rather than the ABI it requires. For
   example, although all video drivers require the video driver
   ABI, not all modules that require the video driver ABI are
   video drivers. This distinction can be made with the
   moduleclass. Currently pre-defined module classes are:

                      MOD_CLASS_NONE
                      MOD_CLASS_VIDEODRV
                      MOD_CLASS_XINPUT
                      MOD_CLASS_EXTENSION

   checksum

   Not currently used.

   The module version information, and the optional SetupProc and
   TearDownProc entry points are found by the loader by locating a
   data object in the module called "modnameModuleData", where
   "modname" is the canonical name of the module. Modules must
   contain such a data object, and it must be declared with global
   scope, be compile-time initialised, and is of the following
   type:
typedef struct {
    XF86ModuleVersionInfo *     vers;
    ModuleSetupProc             setup;
    ModuleTearDownProc          teardown;
} XF86ModuleData;

   The vers parameter must be initialised to a pointer to a
   correctly initialised XF86ModuleVersionInfo struct. The other
   two parameter are optional, and should be initialised to NULL
   when not required. The other parameters are defined as

    typedef pointer (*ModuleSetupProc)(pointer, pointer, int *, int *);

    typedef void (*ModuleTearDownProc)(pointer);

    pointer SetupProc(pointer module, pointer options,
                      int *errmaj, int *errmin);

     When defined, this function is called by the loader after
     successfully loading a module. module is a handle for the
     newly loaded module, and maybe used by the SetupProc if it
     calls other loader functions that require a reference to it.
     The remaining arguments are those that were passed to the
     LoadModule() (or LoadSubModule()), and are described above.
     When the SetupProc is successful it must return a non-NULL
     value. The loader checks this, and if it is NULL it unloads
     the module and reports the failure to the caller of
     LoadModule(). If the SetupProc does things that need to be
     undone when the module is unloaded, it should define a
     TearDownProc, and return a pointer that the TearDownProc can
     use to undo what has been done.

     When a module is loaded multiple times, the SetupProc is
     called once for each time it is loaded.

    void TearDownProc(pointer tearDownData);

     When defined, this function is called when the loader
     unloads a module. The tearDownData parameter is the return
     value of the SetupProc() that was called when the module was
     loaded. The purpose of this function is to clean up before
     the module is unloaded (for example, by freeing allocated
     resources).

Public Loader Interface

   The following is the Loader interface that is available to any
   part of the server, and may also be used from within modules.

    pointer LoadSubModule(pointer parent, const char *module,
                          const char **subdirlist, const char **patternl
ist,
                          pointer options, const XF86ModReqInfo * modreq
,
                          int *errmaj, int *errmin);

     This function is like the LoadModule() function described
     above, except that the module loaded is registered as a
     child of the calling module. The parent parameter is the
     calling module's handle. Modules loaded with this function
     are automatically unloaded when the parent module is
     unloaded. The other difference is that the path parameter
     may not be specified. The module search path used for
     modules loaded with this function is the default search path
     as initialised with LoaderSetPath().

    void UnloadSubModule(pointer module);

     This function unloads the module with handle module. If that
     module itself has children, they are also unloaded. It is
     like UnloadModule(), except that it is safe to use for
     unloading child modules.

    pointer LoaderSymbol(const char *symbol);

     This function returns the address of the symbol with name
     symbol. This may be used to locate a module entry point with
     a known name.

    char **LoaderlistDirs(const char **subdirlist,
                          const char **patternlist);

     This function returns a NULL terminated list of canonical
     modules names for modules found in the default module search
     path. The subdirlist and patternlist parameters are as
     described above, and can be used to control the locations
     and names that are searched. If no modules are found, the
     return value is NULL. The returned list should be freed by
     calling LoaderFreeDirList() when it is no longer needed.

    void LoaderFreeDirList(char **list);

     This function frees a module list created by
     LoaderlistDirs().

    void LoaderReqSymLists(const char **list0, ...);

     This function allows the registration of required symbols
     with the loader. It is normally used by a caller of
     LoadSubModule(). If any symbols registered in this way are
     found to be unresolved when LoaderCheckUnresolved() is
     called then LoaderCheckUnresolved() will report a failure.
     The function takes one or more NULL terminated lists of
     symbols. The end of the argument list is indicated by a NULL
     argument.

    void LoaderReqSymbols(const char *sym0, ...);

     This function is like LoaderReqSymLists() except that its
     arguments are symbols rather than lists of symbols. This
     function is more convenient when single functions are to be
     registered, especially when the single function might depend
     on runtime factors. The end of the argument list is
     indicated by a NULL argument.

    void LoaderRefSymLists(const char **list0, ...);

     This function allows the registration of possibly unresolved
     symbols with the loader. When LoaderCheckUnresolved() is run
     it won't generate warnings for symbols registered in this
     way unless they were also registered as required symbols.
     The function takes one or more NULL terminated lists of
     symbols. The end of the argument list is indicated by a NULL
     argument.

    void LoaderRefSymbols(const char *sym0, ...);

     This function is like LoaderRefSymLists() except that its
     arguments are symbols rather than lists of symbols. This
     function is more convenient when single functions are to be
     registered, especially when the single function might depend
     on runtime factors. The end of the argument list is
     indicated by a NULL argument.

    int LoaderCheckUnresolved(int delayflag);

     This function checks for unresolved symbols. It generates
     warnings for unresolved symbols that have not been
     registered with LoaderRefSymLists(), and maps them to a
     dummy function. This behaviour may change in future. If
     unresolved symbols are found that have been registered with
     LoaderReqSymLists() or LoaderReqSymbols() then this function
     returns a non-zero value. If none of these symbols are
     unresolved the return value is zero, indicating success.

     The delayflag parameter should normally be set to
     LD_RESOLV_IFDONE.

    LoaderErrorMsg(const char *name, const char *modname,
                   int errmaj, int errmin);

     This function prints an error message that includes the text
     “Failed to load module”, the module name modname, a message
     specific to the errmaj value, and the value if errmin. If
     name is non-NULL, it is printed as an identifying prefix to
     the message (followed by a “:”).

Special Registration Functions

   The loader contains some functions for registering some classes
   of modules. These may be moved out of the loader at some point.

    void LoadExtensionList(const ExtensionModule ext[]);

     This registers the entry points for the extension array
     identified by ext. The ExtensionModule struct is defined as:
typedef struct {
    InitExtension       initFunc;
    char *              name;
    Bool                *disablePtr;
} ExtensionModule;

Helper Functions

   This section describe “helper” functions that video driver
   might find useful. While video drivers are not required to use
   any of these to be considered “compliant”, the use of
   appropriate helpers is strongly encouraged to improve the
   consistency of driver behaviour.

Functions for printing messages

    ErrorF(const char *format, ...);

     This is the basic function for writing to the error log
     (typically stderr and/or a log file). Video drivers should
     usually avoid using this directly in favour of the more
     specialised functions described below. This function is
     useful for printing messages while debugging a driver.

    FatalError(const char *format, ...);

     This prints a message and causes the Xserver to abort. It
     should rarely be used within a video driver, as most error
     conditions should be flagged by the return values of the
     driver functions. This allows the higher layers to decide
     how to proceed. In rare cases, this can be used within a
     driver if a fatal unexpected condition is found.

    xf86ErrorF(const char *format, ...);

     This is like ErrorF(), except that the message is only
     printed when the Xserver's verbosity level is set to the
     default (1) or higher. It means that the messages are not
     printed when the server is started with the -quiet flag.
     Typically this function would only be used for continuing
     messages started with one of the more specialised functions
     described below.

    xf86ErrorFVerb(int verb, const char *format, ...);

     Like xf86ErrorF(), except the minimum verbosity level for
     which the message is to be printed is given explicitly.
     Passing a verb value of zero means the message is always
     printed. A value higher than 1 can be used for information
     would normally not be needed, but which might be useful when
     diagnosing problems.

    xf86Msg(MessageType type, const char *format, ...);

     This is like xf86ErrorF(), except that the message is
     prefixed with a marker determined by the value of type. The
     marker is used to indicate the type of message (warning,
     error, probed value, config value, etc). Note the
     xf86Verbose value is ignored for messages of type X_ERROR.

     The marker values are:

   X_PROBED

                    Value was probed.

   X_CONFIG

                    Value was given in the config file.

   X_DEFAULT

                    Value is a default.

   X_CMDLINE

                    Value was given on the command line.

   X_NOTICE

                    Notice.

   X_ERROR

                    Error message.

   X_WARNING

                    Warning message.

   X_INFO

                    Informational message.

   X_NONE

                    No prefix.

   X_NOT_IMPLEMENTED

                    The message relates to functionality that is not
                    yetimplemented.

    xf86MsgVerb(MessageType type, int verb, const char *format, ...);

     Like xf86Msg(), but with the verbosity level given
     explicitly.

    xf86DrvMsg(int scrnIndex, MessageType type, const char *format, ...)
;

     This is like xf86Msg() except that the driver's name (the
     name field of the ScrnInfoRec) followed by the scrnIndex in
     parentheses is printed following the prefix. This should be
     used by video drivers in most cases as it clearly indicates
     which driver/screen the message is for. If scrnIndex is
     negative, this function behaves exactly like xf86Msg().

     NOTE: This function can only be used after the ScrnInfoRec
     and its name field have been allocated. Normally, this means
     that it can not be used before the END of the ChipProbe()
     function. Prior to that, use xf86Msg(), providing the
     driver's name explicitly. No screen number can be supplied
     at that point.

    xf86DrvMsgVerb(int scrnIndex, MessageType type, int verb,
                                const char *format, ...);

     Like xf86DrvMsg(), but with the verbosity level given
     explicitly.

Functions for setting values based on command line and config file

    Bool xf86SetDepthBpp(ScrnInfoPtr scrp, int depth, int bpp,

                                int fbbpp, int depth24flags);

     This function sets the depth, pixmapBPP and bitsPerPixel
     fields of the ScrnInfoRec. It also determines the defaults
     for display-wide attributes and pixmap formats the screen
     will support, and finds the Display subsection that matches
     the depth/bpp. This function should normally be called very
     early from the ChipPreInit() function.

     It requires that the confScreen field of the ScrnInfoRec be
     initialised prior to calling it. This is done by the XFree86
     common layer prior to calling ChipPreInit().

     The parameters passed are:

   depth

   driver's preferred default depth if no other is given. If zero,
   use the overall server default.

   bpp

   Same, but for the pixmap bpp.

   fbbpp

   Same, but for the framebuffer bpp.

   depth24flags

   Flags that indicate the level of 24/32bpp support and whether
   conversion between different framebuffer and pixmap formats is
   supported. The flags for this argument are defined as follows,
   and multiple flags may be ORed together:

   NoDepth24Support

                       No depth 24 formats supported

   Support24bppFb

                       24bpp framebuffer supported

   Support32bppFb

                       32bpp framebuffer supported

   SupportConvert24to32

                       Can convert 24bpp pixmap to 32bpp fb

   SupportConvert32to24

                       Can convert 32bpp pixmap to 24bpp fb

   ForceConvert24to32

                       Force 24bpp pixmap to 32bpp fb conversion

   ForceConvert32to24

                       Force 32bpp pixmap to 24bpp fb conversion

     It uses the command line, config file, and default values in
     the correct order of precedence to determine the depth and
     bpp values. It is up to the driver to check the results to
     see that it supports them. If not the ChipPreInit() function
     should return FALSE.

     If only one of depth/bpp is given, the other is set to a
     reasonable (and consistent) default.

     If a driver finds that the initial depth24flags it uses
     later results in a fb format that requires more video memory
     than is available it may call this function a second time
     with a different depth24flags setting.

     On success, the return value is TRUE. On failure it prints
     an error message and returns FALSE.

     The following fields of the ScrnInfoRec are initialised by
     this function:

     depth, bitsPerPixel, display, imageByteOrder,
     bitmapScanlinePad, bitmapScanlineUnit, bitmapBitOrder,
     numFormats, formats, fbFormat.

    void xf86PrintDepthBpp(scrnInfoPtr scrp);

     This function can be used to print out the depth and bpp
     settings. It should be called after the final call to
     xf86SetDepthBpp().

    Bool xf86SetWeight(ScrnInfoPtr scrp, rgb weight, rgb mask);

     This function sets the weight, mask, offset and rgbBits
     fields of the ScrnInfoRec. It would normally be called
     fairly early in the ChipPreInit() function for
     depths > 8bpp.

     It requires that the depth and display fields of the
     ScrnInfoRec be initialised prior to calling it.

     The parameters passed are:

   weight

         driver's preferred default weight if no other is given. If
         zero, use the overall server default.

   mask

         Same, but for mask.

     It uses the command line, config file, and default values in
     the correct order of precedence to determine the weight
     value. It derives the mask and offset values from the weight
     and the defaults. It is up to the driver to check the
     results to see that it supports them. If not the
     ChipPreInit() function should return FALSE.

     On success, this function prints a message showing the
     weight values selected, and returns TRUE.

     On failure it prints an error message and returns FALSE.

     The following fields of the ScrnInfoRec are initialised by
     this function:

     weight, mask, offset.

    Bool xf86SetDefaultVisual(ScrnInfoPtr scrp, int visual);

     This function sets the defaultVisual field of the
     ScrnInfoRec. It would normally be called fairly early from
     the ChipPreInit() function.

     It requires that the depth and display fields of the
     ScrnInfoRec be initialised prior to calling it.

     The parameters passed are:

   visual

         driver's preferred default visual if no other is given. If -1,
         use the overall server default.

     It uses the command line, config file, and default values in
     the correct order of precedence to determine the default
     visual value. It is up to the driver to check the result to
     see that it supports it. If not the ChipPreInit() function
     should return FALSE.

     On success, this function prints a message showing the
     default visual selected, and returns TRUE.

     On failure it prints an error message and returns FALSE.

    Bool xf86SetGamma(ScrnInfoPtr scrp, Gamma gamma);

     This function sets the gamma field of the ScrnInfoRec. It
     would normally be called fairly early from the ChipPreInit()
     function in cases where the driver supports gamma
     correction.

     It requires that the monitor field of the ScrnInfoRec be
     initialised prior to calling it.

     The parameters passed are:

   gamma

        driver's preferred default gamma if no other is given. If zero
        (< 0.01), use the overall server default.

     It uses the command line, config file, and default values in
     the correct order of precedence to determine the gamma
     value. It is up to the driver to check the results to see
     that it supports them. If not the ChipPreInit() function
     should return FALSE.

     On success, this function prints a message showing the gamma
     value selected, and returns TRUE.

     On failure it prints an error message and returns FALSE.

    void xf86SetDpi(ScrnInfoPtr pScrn, int x, int y);

     This function sets the xDpi and yDpi fields of the
     ScrnInfoRec. The driver can specify preferred defaults by
     setting x and y to non-zero values. The -dpi command line
     option overrides all other settings. Otherwise, if the
     DisplaySize entry is present in the screen's Monitor config
     file section, it is used together with the virtual size to
     calculate the dpi values. This function should be called
     after all the mode resolution has been done.

    void xf86SetBlackWhitePixels(ScrnInfoPtr pScrn);

     This functions sets the blackPixel and whitePixel fields of
     the ScrnInfoRec according to whether or not the -flipPixels
     command line options is present.

    const char *xf86GetVisualName(int visual);

     Returns a printable string with the visual name matching the
     numerical visual class provided. If the value is outside the
     range of valid visual classes, NULL is returned.

Primary Mode functions

   The primary mode helper functions are those which would
   normally be used by a driver, unless it has unusual
   requirements which cannot be catered for the by the helpers.

    int xf86ValidateModes(ScrnInfoPtr scrp, DisplayModePtr availModes,
                          char **modeNames, ClockRangePtr clockRanges,
                          int *linePitches, int minPitch, int maxPitch,
                          int pitchInc, int minHeight, int maxHeight,
                          int virtualX, int virtualY,
                          unsigned long apertureSize,
                          LookupModeFlags strategy);

     This function basically selects the set of modes to use
     based on those available and the various constraints. It
     also sets some other related parameters. It is normally
     called near the end of the ChipPreInit() function.

     The parameters passed to the function are:

   availModes

   List of modes available for the monitor.

   modeNames

   List of mode names that the screen is requesting.

   clockRanges

   A list of clock ranges allowed by the driver. Each range
   includes whether interlaced or multiscan modes are supported
   for that range. See below for more on clockRanges.

   linePitches

   List of line pitches supported by the driver. This is optional
   and should be NULL when not used.

   minPitch

   Minimum line pitch supported by the driver. This must be
   supplied when linePitches is NULL, and is ignored otherwise.

   maxPitch

   Maximum line pitch supported by the driver. This is required
   when minPitch is required.

   pitchInc

   Granularity of horizontal pitch values as supported by the
   chipset. This is expressed in bits. This must be supplied.

   minHeight

   minimum virtual height allowed. If zero, no limit is imposed.

   maxHeight

   maximum virtual height allowed. If zero, no limit is imposed.

   virtualX

   If greater than zero, this is the virtual width value that will
   be used. Otherwise, the virtual width is chosen to be the
   smallest that can accommodate the modes selected.

   virtualY

   If greater than zero, this is the virtual height value that
   will be used. Otherwise, the virtual height is chosen to be the
   smallest that can accommodate the modes selected.

   apertureSize

   The size (in bytes) of the aperture used to access video
   memory.

   strategy

   The strategy to use when choosing from multiple modes with the
   same name. The options are:

   LOOKUP_DEFAULT

                       ???

   LOOKUP_BEST_REFRESH

                       mode with best refresh rate

   LOOKUP_CLOSEST_CLOCK

                       mode with closest matching clock

   LOOKUP_LIST_ORDER

                       first usable mode in list

   The following options can also be combined (OR'ed) with one of
   the above:

   LOOKUP_CLKDIV2

   Allow halved clocks

   LOOKUP_OPTIONAL_TOLERANCES

   Allow missing horizontal sync and/or vertical refresh ranges in
   the xorg.conf Monitor section

   LOOKUP_OPTIONAL_TOLERANCES should only be specified when the
   driver can ensure all modes it generates can sync on, or at
   least not damage, the monitor or digital flat panel. Horizontal
   sync and/or vertical refresh ranges specified by the user will
   still be honoured (and acted upon).

     This function requires that the following fields of the
     ScrnInfoRec are initialised prior to calling it:

   clock[]

            List of discrete clocks (when non-programmable)

   numClocks

            Number of discrete clocks (when non-programmable)

   progClock

            Whether the clock is programmable or not

   monitor

            Pointer to the applicable xorg.conf monitor section

   fdFormat

            Format of the screen buffer

   videoRam

            total video memory size (in bytes)

   maxHValue

            Maximum horizontal timing value allowed

   maxVValue

            Maximum vertical timing value allowed

   xInc

            Horizontal timing increment in pixels (defaults to 8)

     This function fills in the following ScrnInfoRec fields:

   modePool

   A subset of the modes available to the monitor which are
   compatible with the driver.

   modes

   One mode entry for each of the requested modes, with the status
   field of each filled in to indicate if the mode has been
   accepted or not. This list of modes is a circular list.

   virtualX

   The resulting virtual width.

   virtualY

   The resulting virtual height.

   displayWidth

   The resulting line pitch.

   virtualFrom

   Where the virtual size was determined from.

     The first stage of this function checks that the virtualX
     and virtualY values supplied (if greater than zero) are
     consistent with the line pitch and maxHeight limitations. If
     not, an error message is printed, and the return value is
     -1.

     The second stage sets up the mode pool, eliminating
     immediately any modes that exceed the driver's line pitch
     limits, and also the virtual width and height limits (if
     greater than zero). For each mode removed an informational
     message is printed at verbosity level 2. If the mode pool
     ends up being empty, a warning message is printed, and the
     return value is 0.

     The final stage is to lookup each mode name, and fill in the
     remaining parameters. If an error condition is encountered,
     a message is printed, and the return value is -1. Otherwise,
     the return value is the number of valid modes found (0 if
     none are found).

     Even if the supplied mode names include duplicates, no two
     names will ever match the same mode. Furthermore, if the
     supplied mode names do not yield a valid mode (including the
     case where no names are passed at all), the function will
     continue looking through the mode pool until it finds a mode
     that survives all checks, or until the mode pool is
     exhausted.

     A message is only printed by this function when a
     fundamental problem is found. It is intended that this
     function may be called more than once if there is more than
     one set of constraints that the driver can work within.

     If this function returns -1, the ChipPreInit() function
     should return FALSE.

     clockRanges is a linked list of clock ranges allowed by the
     driver. If a mode doesn't fit in any of the defined
     clockRanges, it is rejected. The first clockRange that
     matches all requirements is used. This structure needs to be
     initialized to NULL when allocated.

     clockRanges contains the following fields:

   minClock, maxClock

   The lower and upper mode clock bounds for which the rest of the
   clockRange parameters apply. Since these are the mode clocks,
   they are not scaled with the ClockMulFactor and ClockDivFactor.
   It is up to the driver to adjust these values if they depend on
   the clock scaling factors.

   clockIndex

   (not used yet) -1 for programmable clocks

   interlaceAllowed

   TRUE if interlacing is allowed for this range

   doubleScanAllowed

   TRUE if doublescan or multiscan is allowed for this range

   ClockMulFactor, ClockDivFactor

   Scaling factors that are applied to the mode clocks ONLY before
   selecting a clock index (when there is no programmable clock)
   or a SynthClock value. This is useful for drivers that support
   pixel multiplexing or that need to scale the clocks because of
   hardware restrictions (like sending 24bpp data to an 8 bit
   RAMDAC using a tripled clock).

   Note that these parameters describe what must be done to the
   mode clock to achieve the data transport clock between graphics
   controller and RAMDAC. For example for 2:1 pixel multiplexing,
   two pixels are sent to the RAMDAC on each clock. This allows
   the RAMDAC clock to be half of the actual pixel clock. Hence,
   ClockMulFactor=1 and ClockDivFactor=2. This means that the
   clock used for clock selection (ie, determining the correct
   clock index from the list of discrete clocks) or for the
   SynthClock field in case of a programmable clock is:
   (mode->Clock * ClockMulFactor) / ClockDivFactor.

   PrivFlags

   This field is copied into the mode->PrivFlags field when this
   clockRange is selected by xf86ValidateModes(). It allows the
   driver to find out what clock range was selected, so it knows
   it needs to set up pixel multiplexing or any other
   range-dependent feature. This field is purely driver-defined:
   it may contain flag bits, an index or anything else (as long as
   it is an INT).

     Note that the mode->SynthClock field is always filled in by
     xf86ValidateModes(): it will contain the “data transport
     clock”, which is the clock that will have to be programmed
     in the chip when it has a programmable clock, or the clock
     that will be picked from the clocks list when it is not a
     programmable one. Thus:
    mode->SynthClock = (mode->Clock * ClockMulFactor) / ClockDivFactor

    void xf86PruneDriverModes(ScrnInfoPtr scrp);

     This function deletes modes in the modes field of the
     ScrnInfoRec that have been marked as invalid. This is
     normally run after having run xf86ValidateModes() for the
     last time. For each mode that is deleted, a warning message
     is printed out indicating the reason for it being deleted.

    void xf86SetCrtcForModes(ScrnInfoPtr scrp, int adjustFlags);

     This function fills in the Crtc* fields for all the modes in
     the modes field of the ScrnInfoRec. The adjustFlags
     parameter determines how the vertical CRTC values are scaled
     for interlaced modes. They are halved if it is
     INTERLACE_HALVE_V. The vertical CRTC values are doubled for
     doublescan modes, and are further multiplied by the VScan
     value.

     This function is normally called after calling
     xf86PruneDriverModes().

    void xf86PrintModes(ScrnInfoPtr scrp);

     This function prints out the virtual size setting, and the
     line pitch being used. It also prints out two lines for each
     mode being used. The first line includes the mode's pixel
     clock, horizontal sync rate, refresh rate, and whether it is
     interlaced, doublescanned and/or multi-scanned. The second
     line is the mode's Modeline.

     This function is normally called after calling
     xf86SetCrtcForModes().

Secondary Mode functions

   The secondary mode helper functions are functions which are
   normally used by the primary mode helper functions, and which
   are not normally called directly by a driver. If a driver has
   unusual requirements and needs to do its own mode validation,
   it might be able to make use of some of these secondary mode
   helper functions.

    const char *xf86ModeStatusToString(ModeStatus status);

     This function converts the status value to a descriptive
     printable string.

    void xf86DeleteMode(DisplayModePtr *modeList, DisplayModePtr mode);

     This function deletes the mode given from the modeList. It
     never prints any messages, so it is up to the caller to
     print a message if required.

Functions for handling strings and tokens

   Tables associating strings and numerical tokens combined with
   the following functions provide a compact way of handling
   strings from the config file, and for converting tokens into
   printable strings. The table data structure is:
typedef struct {
    int                 token;
    const char *        name;
} SymTabRec, *SymTabPtr;

   A table is an initialised array of SymTabRec. The tokens must
   be non-negative integers. Multiple names may be mapped to a
   single token. The table is terminated with an element with a
   token value of -1 and NULL for the name.

    const char *xf86TokenToString(SymTabPtr table, int token);

     This function returns the first string in table that matches
     token. If no match is found, NULL is returned (NOTE, older
     versions of this function would return the string "unknown"
     when no match is found).

    int xf86StringToToken(SymTabPtr table, const char *string);

     This function returns the first token in table that matches
     string. The xf86NameCmp() function is used to determine the
     match. If no match is found, -1 is returned.

Functions for finding which config file entries to use

   These functions can be used to select the appropriate config
   file entries that match the detected hardware. They are
   described above in the Probe and Available Functions sections.

Probing discrete clocks on old hardware

   The xf86GetClocks() function may be used to assist in finding
   the discrete pixel clock values on older hardware.

    void xf86GetClocks(ScrnInfoPtr pScrn, int num,
                       Bool (*ClockFunc)(ScrnInfoPtr, int),
                       void (*ProtectRegs)(ScrnInfoPtr, Bool),
                       void (*BlankScreen)(ScrnInfoPtr, Bool),
                       int vertsyncreg, int maskval, int knownclkindex,
                       int knownclkvalue);

     This function uses a comparative sampling method to measure
     the discrete pixel clock values. The number of discrete
     clocks to measure is given by num. clockFunc is a function
     that selects the n'th clock. It should also save or restore
     any state affected by programming the clocks when the index
     passed is CLK_REG_SAVE or CLK_REG_RESTORE. ProtectRegs is a
     function that does whatever is required to protect the
     hardware state while selecting a new clock. BlankScreen is a
     function that blanks the screen. vertsyncreg and maskval are
     the register and bitmask to check for the presence of
     vertical sync pulses. knownclkindex and knownclkvalue are
     the index and value of a known clock. These are the known
     references on which the comparative measurements are based.
     The number of clocks probed is set in pScrn->numClocks, and
     the probed clocks are set in the pScrn->clock[] array. All
     of the clock values are in units of kHz.

    void xf86ShowClocks(ScrnInfoPtr scrp, MessageType from);

     Print out the pixel clocks scrp->clock[]. from indicates
     whether the clocks were probed or from the config file.

Other helper functions

    Bool xf86IsUnblank(int mode);

     Returns TRUE when the screen saver mode specified by mode
     requires the screen be unblanked, and FALSE otherwise. The
     screen saver modes that require blanking are SCREEN_SAVER_ON
     and SCREEN_SAVER_CYCLE, and the screen saver modes that
     require unblanking are SCREEN_SAVER_OFF and
     SCREEN_SAVER_FORCER. Drivers may call this helper from their
     SaveScreen() function to interpret the screen saver modes.

The vgahw module

   The vgahw modules provides an interface for saving, restoring
   and programming the standard VGA registers, and for handling
   VGA colourmaps.

Data Structures

   The public data structures used by the vgahw module are
   vgaRegRec and vgaHWRec. They are defined in vgaHW.h.

General vgahw Functions

    Bool vgaHWGetHWRec(ScrnInfoPtr pScrn);

     This function allocates a vgaHWRec structure, and hooks it
     into the ScrnInfoRec's privates. Like all information hooked
     into the privates, it is persistent, and only needs to be
     allocated once per screen. This function should normally be
     called from the driver's ChipPreInit() function. The
     vgaHWRec is zero-allocated, and the following fields are
     explicitly initialised:

   ModeReg.DAC[]

   initialised with a default colourmap

   ModeReg.Attribute[0x11]

   initialised with the default overscan index

   ShowOverscan

   initialised according to the "ShowOverscan" option

   paletteEnabled

   initialised to FALSE

   cmapSaved

   initialised to FALSE

   pScrn

   initialised to pScrn

     In addition to the above, vgaHWSetStdFuncs() is called to
     initialise the register access function fields with the
     standard VGA set of functions.

     Once allocated, a pointer to the vgaHWRec can be obtained
     from the ScrnInfoPtr with the VGAHWPTR(pScrn) macro.

    void vgaHWFreeHWRec(ScrnInfoPtr pScrn);

     This function frees a vgaHWRec structure. It should be
     called from a driver's ChipFreeScreen() function.

    Bool vgaHWSetRegCounts(ScrnInfoPtr pScrn, int numCRTC,
                          int numSequencer, int numGraphics, int numAttr
ibute);

     This function allows the number of CRTC, Sequencer, Graphics
     and Attribute registers to be changed. This makes it
     possible for extended registers to be saved and restored
     with vgaHWSave() and vgaHWRestore(). This function should be
     called after a vgaHWRec has been allocated with
     vgaHWGetHWRec(). The default values are defined in vgaHW.h
     as follows:
#define VGA_NUM_CRTC 25
#define VGA_NUM_SEQ   5
#define VGA_NUM_GFX   9
#define VGA_NUM_ATTR 21

    Bool vgaHWCopyReg(vgaRegPtr dst, vgaRegPtr src);

     This function copies the contents of the VGA saved registers
     in src to dst. Note that it isn't possible to simply do this
     with memcpy() (or similar). This function returns TRUE
     unless there is a problem allocating space for the CRTC and
     related fields in dst.

    void vgaHWSetStdFuncs(vgaHWPtr hwp);

     This function initialises the register access function
     fields of hwp with the standard VGA set of functions. This
     is called by vgaHWGetHWRec(), so there is usually no need to
     call this explicitly. The register access functions are
     described below. If the registers are shadowed in some other
     port I/O space (for example a PCI I/O region), these
     functions can be used to access the shadowed registers if
     hwp->PIOOffset is initialised with offset, calculated in
     such a way that when the standard VGA I/O port value is
     added to it the correct offset into the PIO area results.
     This value is initialised to zero in vgaHWGetHWRec(). (Note:
     the PIOOffset functionality is present in XFree86 4.1.0 and
     later.)

    void vgaHWSetMmioFuncs(vgaHWPtr hwp, CARD8 *base, int offset);

     This function initialised the register access function
     fields of hwp with a generic MMIO set of functions.
     hwp->MMIOBase is initialised with base, which must be the
     virtual address that the start of MMIO area is mapped to.
     hwp->MMIOOffset is initialised with offset, which must be
     calculated in such a way that when the standard VGA I/O port
     value is added to it the correct offset into the MMIO area
     results. That means that these functions are only suitable
     when the VGA I/O ports are made available in a direct
     mapping to the MMIO space. If that is not the case, the
     driver will need to provide its own register access
     functions. The register access functions are described
     below.

    Bool vgaHWMapMem(ScrnInfoPtr pScrn);

     This function maps the VGA memory window. It requires that
     the vgaHWRec be allocated. If a driver requires non-default
     MapPhys or MapSize settings (the physical location and size
     of the VGA memory window) then those fields of the vgaHWRec
     must be initialised before calling this function. Otherwise,
     this function initialiases the default values of 0xA0000 for
     MapPhys and (64 * 1024) for MapSize. This function must be
     called before attempting to save or restore the VGA state.
     If the driver doesn't call it explicitly, the vgaHWSave()
     and vgaHWRestore() functions may call it if they need to
     access the VGA memory (in which case they will also call
     vgaHWUnmapMem() to unmap the VGA memory before exiting).

    void vgaHWUnmapMem(ScrnInfoPtr pScrn);

     This function unmaps the VGA memory window. It must only be
     called after the memory has been mapped. The Base field of
     the vgaHWRec field is set to NULL to indicate that the
     memory is no longer mapped.

    void vgaHWGetIOBase(vgaHWPtr hwp);

     This function initialises the IOBase field of the vgaHWRec.
     This function must be called before using any other
     functions that access the video hardware.

     A macro VGAHW_GET_IOBASE() is also available in vgaHW.h that
     returns the I/O base, and this may be used when the vgahw
     module is not loaded (for example, in the ChipProbe()
     function).

    void vgaHWUnlock(vgaHWPtr hwp);

     This function unlocks the VGA CRTC[0-7] registers, and must
     be called before attempting to write to those registers.

    void vgaHWLock(vgaHWPtr hwp);

     This function locks the VGA CRTC[0-7] registers.

    void vgaHWEnable(vgaHWPtr hwp);

     This function enables the VGA subsystem. (Note, this
     function is present in XFree86 4.1.0 and later.).

    void vgaHWDisable(vgaHWPtr hwp);

     This function disables the VGA subsystem. (Note, this
     function is present in XFree86 4.1.0 and later.).

    void vgaHWSave(ScrnInfoPtr pScrn, vgaRegPtr save, int flags);

     This function saves the VGA state. The state is written to
     the vgaRegRec pointed to by save. flags is set to one or
     more of the following flags ORed together:

   VGA_SR_MODE

               the mode setting registers are saved

   VGA_SR_FONTS

               the text mode font/text data is saved

   VGA_SR_CMAP

               the colourmap (LUT) is saved

   VGA_SR_ALL

               all of the above are saved

     The vgaHWRec and its IOBase fields must be initialised
     before this function is called. If VGA_SR_FONTS is set in
     flags, the VGA memory window must be mapped. If it isn't
     then vgaHWMapMem() will be called to map it, and
     vgaHWUnmapMem() will be called to unmap it afterwards.
     vgaHWSave() uses the three functions below in the order
     vgaHWSaveColormap(), vgaHWSaveMode(), vgaHWSaveFonts() to
     carry out the different save phases. It is undecided at this
     stage whether they will remain part of the vgahw module's
     public interface or not.

    void vgaHWSaveMode(ScrnInfoPtr pScrn, vgaRegPtr save);

     This function saves the VGA mode registers. They are saved
     to the vgaRegRec pointed to by save. The registers saved
     are:

           MiscOut
           CRTC[0-0x18]
           Attribute[0-0x14]
           Graphics[0-8]
           Sequencer[0-4]

     The number of registers actually saved may be modified by a
     prior call to vgaHWSetRegCounts().

    void vgaHWSaveFonts(ScrnInfoPtr pScrn, vgaRegPtr save);

     This function saves the text mode font and text data held in
     the video memory. If called while in a graphics mode, no
     save is done. The VGA memory window must be mapped with
     vgaHWMapMem() before to calling this function.

     On some platforms, one or more of the font/text plane saves
     may be no-ops. This is the case when the platform's VC
     driver already takes care of this.

    void vgaHWSaveColormap(ScrnInfoPtr pScrn, vgaRegPtr save);

     This function saves the VGA colourmap (LUT). Before saving
     it, it attempts to verify that the colourmap is readable. In
     rare cases where it isn't readable, a default colourmap is
     saved instead.

    void vgaHWRestore(ScrnInfoPtr pScrn, vgaRegPtr restore, int flags);

     This function programs the VGA state. The state programmed
     is that contained in the vgaRegRec pointed to by restore.
     flags is the same as described above for the vgaHWSave()
     function.

     The vgaHWRec and its IOBase fields must be initialised
     before this function is called. If VGA_SR_FONTS is set in
     flags, the VGA memory window must be mapped. If it isn't
     then vgaHWMapMem() will be called to map it, and
     vgaHWUnmapMem() will be called to unmap it afterwards.
     vgaHWRestore() uses the three functions below in the order
     vgaHWRestoreFonts(), vgaHWRestoreMode(),
     vgaHWRestoreColormap() to carry out the different restore
     phases. It is undecided at this stage whether they will
     remain part of the vgahw module's public interface or not.

    void vgaHWRestoreMode(ScrnInfoPtr pScrn, vgaRegPtr restore);

     This function restores the VGA mode registers. They are
     restored from the data in the vgaRegRec pointed to by
     restore. The registers restored are:

           MiscOut
           CRTC[0-0x18]
           Attribute[0-0x14]
           Graphics[0-8]
           Sequencer[0-4]

     The number of registers actually restored may be modified by
     a prior call to vgaHWSetRegCounts().

    void vgaHWRestoreFonts(ScrnInfoPtr pScrn, vgaRegPtr restore);

     This function restores the text mode font and text data to
     the video memory. The VGA memory window must be mapped with
     vgaHWMapMem() before to calling this function.

     On some platforms, one or more of the font/text plane
     restores may be no-ops. This is the case when the platform's
     VC driver already takes care of this.

    void vgaHWRestoreColormap(ScrnInfoPtr pScrn, vgaRegPtr restore);

     This function restores the VGA colourmap (LUT).

    void vgaHWInit(ScrnInfoPtr pScrn, DisplayModePtr mode);

     This function fills in the vgaHWRec's ModeReg field with the
     values appropriate for programming the given video mode. It
     requires that the ScrnInfoRec's depth field is initialised,
     which determines how the registers are programmed.

    void vgaHWSeqReset(vgaHWPtr hwp, Bool start);

     Do a VGA sequencer reset. If start is TRUE, the reset is
     started. If start is FALSE, the reset is ended.

    void vgaHWProtect(ScrnInfoPtr pScrn, Bool on);

     This function protects VGA registers and memory from
     corruption during loads. It is typically called with on set
     to TRUE before programming, and with on set to FALSE after
     programming.

    Bool vgaHWSaveScreen(ScreenPtr pScreen, int mode);

     This function blanks and unblanks the screen. It is blanked
     when mode is SCREEN_SAVER_ON or SCREEN_SAVER_CYCLE, and
     unblanked when mode is SCREEN_SAVER_OFF or
     SCREEN_SAVER_FORCER.

    void vgaHWBlankScreen(ScrnInfoPtr pScrn, Bool on);

     This function blanks and unblanks the screen. It is blanked
     when on is FALSE, and unblanked when on is TRUE. This
     function is provided for use in cases where the ScrnInfoRec
     can't be derived from the ScreenRec (while probing for
     clocks, for example).

VGA Colormap Functions

   The vgahw module uses the standard colormap support (see the
   Colormap Handling section. This is initialised with the
   following function:

    Bool vgaHWHandleColormaps(ScreenPtr pScreen);

VGA Register Access Functions

   The vgahw module abstracts access to the standard VGA registers
   by using a set of functions held in the vgaHWRec. When the
   vgaHWRec is created these function pointers are initialised
   with the set of standard VGA I/O register access functions. In
   addition to these, the vgahw module includes a basic set of
   MMIO register access functions, and the vgaHWRec function
   pointers can be initialised to these by calling the
   vgaHWSetMmioFuncs() function described above. Some
   drivers/platforms may require a different set of functions for
   VGA access. The access functions are described here.

    void writeCrtc(vgaHWPtr hwp, CARD8 index, CARD8 value);

     Write value to CRTC register index.

    CARD8 readCrtc(vgaHWPtr hwp, CARD8 index);

     Return the value read from CRTC register index.

    void writeGr(vgaHWPtr hwp, CARD8 index, CARD8 value);

     Write value to Graphics Controller register index.

    CARD8 readGR(vgaHWPtr hwp, CARD8 index);

     Return the value read from Graphics Controller register
     index.

    void writeSeq(vgaHWPtr hwp, CARD8 index, CARD8, value);

     Write value to Sequencer register index.

    CARD8 readSeq(vgaHWPtr hwp, CARD8 index);

     Return the value read from Sequencer register index.

    void writeAttr(vgaHWPtr hwp, CARD8 index, CARD8, value);

     Write value to Attribute Controller register index. When
     writing out the index value this function should set bit 5
     (0x20) according to the setting of hwp->paletteEnabled in
     order to preserve the palette access state. It should be
     cleared when hwp->paletteEnabled is TRUE and set when it is
     FALSE.

    CARD8 readAttr(vgaHWPtr hwp, CARD8 index);

     Return the value read from Attribute Controller register
     index. When writing out the index value this function should
     set bit 5 (0x20) according to the setting of
     hwp->paletteEnabled in order to preserve the palette access
     state. It should be cleared when hwp->paletteEnabled is TRUE
     and set when it is FALSE.

    void writeMiscOut(vgaHWPtr hwp, CARD8 value);

     Write “value” to the Miscellaneous Output register.

    CARD8 readMiscOut(vgwHWPtr hwp);

     Return the value read from the Miscellaneous Output
     register.

    void enablePalette(vgaHWPtr hwp);

     Clear the palette address source bit in the Attribute
     Controller index register and set hwp->paletteEnabled to
     TRUE.

    void disablePalette(vgaHWPtr hwp);

     Set the palette address source bit in the Attribute
     Controller index register and set hwp->paletteEnabled to
     FALSE.

    void writeDacMask(vgaHWPtr hwp, CARD8 value);

     Write value to the DAC Mask register.

    CARD8 readDacMask(vgaHWptr hwp);

     Return the value read from the DAC Mask register.

    void writeDacReadAddress(vgaHWPtr hwp, CARD8 value);

     Write value to the DAC Read Address register.

    void writeDacWriteAddress(vgaHWPtr hwp, CARD8 value);

     Write value to the DAC Write Address register.

    void writeDacData(vgaHWPtr hwp, CARD8 value);

     Write value to the DAC Data register.

    CARD8 readDacData(vgaHWptr hwp);

     Return the value read from the DAC Data register.

    CARD8 readEnable(vgaHWptr hwp);

     Return the value read from the VGA Enable register. (Note:
     This function is present in XFree86 4.1.0 and later.)

    void writeEnable(vgaHWPtr hwp, CARD8 value);

     Write value to the VGA Enable register. (Note: This function
     is present in XFree86 4.1.0 and later.)

Some notes about writing a driver

Note

   NOTE: some parts of this are not up to date

   The following is an outline for writing a basic unaccelerated
   driver for a PCI video card with a linear mapped framebuffer,
   and which has a VGA core. It is includes some general
   information that is relevant to most drivers (even those which
   don't fit that basic description).

   The information here is based on the initial conversion of the
   Matrox Millennium driver to the “new design”. For a fleshing
   out and sample implementation of some of the bits outlined
   here, refer to that driver. Note that this is an example only.
   The approach used here will not be appropriate for all drivers.

   Each driver must reserve a unique driver name, and a string
   that is used to prefix all of its externally visible symbols.
   This is to avoid name space clashes when loading multiple
   drivers. The examples here are for the “ZZZ” driver, which uses
   the “ZZZ” or “zzz” prefix for its externally visible symbols.

Include files

   All drivers normally include the following headers:

       "xf86.h"
       "xf86_OSproc.h"
       "xf86_ansic.h"
       "xf86Resources.h"

   Wherever inb/outb (and related things) are used the following
   should be included:

       "compiler.h"

   Note: in drivers, this must be included after "xf86_ansic.h".

   Drivers that need to access PCI vendor/device definitions need
   this:

       "xf86PciInfo.h"

   Drivers that need to access the PCI config space need this:

       "xf86Pci.h"

   Drivers using the mi banking wrapper need:

       "mibank.h"

   Drivers that initialise a SW cursor need this:

       "mipointer.h"

   All drivers using the mi colourmap code need this:

       "micmap.h"

   If a driver uses the vgahw module, it needs this:

       "vgaHW.h"

   Drivers supporting VGA or Hercules monochrome screens need:

       "xf1bpp.h"

   Drivers supporting VGA or EGC 16-colour screens need:

       "xf4bpp.h"

   Drivers using cfb need:
    #define PSZ 8
    #include "cfb.h"
    #undef PSZ

   Drivers supporting bpp 16, 24 or 32 with cfb need one or more
   of:

       "cfb16.h"
       "cfb24.h"
       "cfb32.h"

   The driver's own header file:

       "zzz.h"

   Drivers must NOT include the following:

       "xf86Priv.h"
       "xf86Privstr.h"
       "xf86_libc.h"
       "xf86_OSlib.h"
       "Xos.h"
       any OS header

Data structures and initialisation

     * The following macros should be defined:
#define VERSION <version-as-an-int>
#define ZZZ_NAME "ZZZ"         /* the name used to prefix messages */
#define ZZZ_DRIVER_NAME "zzz"  /* the driver name as used in config file
 */
#define ZZZ_MAJOR_VERSION <int>
#define ZZZ_MINOR_VERSION <int>
#define ZZZ_PATCHLEVEL    <int>

       NOTE: ZZZ_DRIVER_NAME should match the name of the driver
       module without things like the "lib" prefix, the "_drv"
       suffix or filename extensions.
     * A DriverRec must be defined, which includes the functions
       required at the pre-probe phase. The name of this DriverRec
       must be an upper-case version of ZZZ_DRIVER_NAME (for the
       purposes of static linking).
DriverRec ZZZ = {
    VERSION,
    ZZZ_DRIVER_NAME,
    ZZZIdentify,
    ZZZProbe,
    ZZZAvailableOptions,
    NULL,
    0
};

     * Define list of supported chips and their matching ID:
static SymTabRec ZZZChipsets[] = {
    { PCI_CHIP_ZZZ1234, "zzz1234a" },
    { PCI_CHIP_ZZZ5678, "zzz5678a" },
    { -1,               NULL }
};

       The token field may be any integer value that the driver
       may use to uniquely identify the supported chipsets. For
       drivers that support only PCI devices using the PCI device
       IDs might be a natural choice, but this isn't mandatory.
       For drivers that support both PCI and other devices (like
       ISA), some other ID should probably used. When other IDs
       are used as the tokens it is recommended that the names be
       defined as an enum type.
     * If the driver uses the xf86MatchPciInstances() helper
       (recommended for drivers that support PCI cards) a list
       that maps PCI IDs to chip IDs and fixed resources must be
       defined:
static PciChipsets ZZZPciChipsets[] = {
    { PCI_CHIP_ZZZ1234, PCI_CHIP_ZZZ1234, RES_SHARED_VGA },
    { PCI_CHIP_ZZZ5678, PCI_CHIP_ZZZ5678, RES_SHARED_VGA },
    { -1,               -1,               RES_UNDEFINED }
}

     * Define the XF86ModuleVersionInfo struct for the driver.
       This is required for the dynamically loaded version:
static XF86ModuleVersionInfo zzzVersRec =
{
    "zzz",
    MODULEVENDORSTRING,
    MODINFOSTRING1,
    MODINFOSTRING2,
    XF86_VERSION_CURRENT,
    ZZZ_MAJOR_VERSION, ZZZ_MINOR_VERSION, ZZZ_PATCHLEVEL,
    ABI_CLASS_VIDEODRV,
    ABI_VIDEODRV_VERSION,
    MOD_CLASS_VIDEODRV,
    {0,0,0,0}
};

     * Define a data structure to hold the driver's
       screen-specific data. This must be used instead of global
       variables. This would be defined in the "zzz.h" file,
       something like:
typedef struct {
    type1  field1;
    type2  field2;
    int    fooHack;
    Bool   pciRetry;
    Bool   noAccel;
    Bool   hwCursor;
    CloseScreenProcPtr CloseScreen;
    OptionInfoPtr Options;
    ...
} ZZZRec, *ZZZPtr;

     * Define the list of config file Options that the driver
       accepts. For consistency between drivers those in the list
       of “standard” options should be used where appropriate
       before inventing new options.
typedef enum {
    OPTION_FOO_HACK,
    OPTION_PCI_RETRY,
    OPTION_HW_CURSOR,
    OPTION_NOACCEL
} ZZZOpts;

static const OptionInfoRec ZZZOptions[] = {
  { OPTION_FOO_HACK,  "FooHack",   OPTV_INTEGER, {0}, FALSE },
  { OPTION_PCI_RETRY, "PciRetry",  OPTV_BOOLEAN, {0}, FALSE },
  { OPTION_HW_CURSOR, "HWcursor",  OPTV_BOOLEAN, {0}, FALSE },
  { OPTION_NOACCEL,   "NoAccel",   OPTV_BOOLEAN, {0}, FALSE },
  { -1,               NULL,        OPTV_NONE,    {0}, FALSE }
};

Functions

SetupProc

   For dynamically loaded modules, a ModuleData variable is
   required. It is should be the name of the driver prepended to
   "ModuleData". A Setup() function is also required, which calls
   xf86AddDriver() to add the driver to the main list of drivers.
static MODULESETUPPROTO(zzzSetup);

XF86ModuleData zzzModuleData = { &zzzVersRec, zzzSetup, NULL };

static pointer
zzzSetup(pointer module, pointer opts, int *errmaj, int *errmin)
{
    static Bool setupDone = FALSE;

    /* This module should be loaded only once, but check to be sure. */

    if (!setupDone) {
        /*
         * Modules that this driver always requires may be loaded
         * here  by calling LoadSubModule().
         */

        setupDone = TRUE;
        xf86AddDriver(&MGA, module, 0);

        /*
         * The return value must be non-NULL on success even though
         * there is no TearDownProc.
         */
        return (pointer)1;
    } else {
        if (errmaj) *errmaj = LDR_ONCEONLY;
        return NULL;
    }
}

GetRec, FreeRec

   A function is usually required to allocate the driver's
   screen-specific data structure and hook it into the
   ScrnInfoRec's driverPrivate field. The ScrnInfoRec's
   driverPrivate is initialised to NULL, so it is easy to check if
   the initialisation has already been done. After allocating it,
   initialise the fields. By using xnfcalloc() to do the
   allocation it is zeroed, and if the allocation fails the server
   exits.

   NOTE: When allocating structures from inside the driver which
   are defined on the common level it is important to initialize
   the structure to zero. Only this guarantees that the server
   remains source compatible to future changes in common level
   structures.
static Bool
ZZZGetRec(ScrnInfoPtr pScrn)
{
    if (pScrn->driverPrivate != NULL)
        return TRUE;
    pScrn->driverPrivate = xnfcalloc(sizeof(ZZZRec), 1);
    /* Initialise as required */
    ...
    return TRUE;
}

   Define a macro in "zzz.h" which gets a pointer to the ZZZRec
   when given pScrn:
#define ZZZPTR(p) ((ZZZPtr)((p)->driverPrivate))

   Define a function to free the above, setting it to NULL once it
   has been freed:
static void
ZZZFreeRec(ScrnInfoPtr pScrn)
{
    if (pScrn->driverPrivate == NULL)
        return;
    xfree(pScrn->driverPrivate);
    pScrn->driverPrivate = NULL;
}

Identify

   Define the Identify() function. It is run before the Probe, and
   typically prints out an identifying message, which might
   include the chipsets it supports. This function is mandatory:
static void
ZZZIdentify(int flags)
{
    xf86PrintChipsets(ZZZ_NAME, "driver for ZZZ Tech chipsets",
                      ZZZChipsets);
}

Probe

   Define the Probe() function. The purpose of this is to find all
   instances of the hardware that the driver supports, and for the
   ones not already claimed by another driver, claim the slot, and
   allocate a ScrnInfoRec. This should be a minimal probe, and it
   should under no circumstances leave the state of the hardware
   changed. Because a device is found, don't assume that it will
   be used. Don't do any initialisations other than the required
   ScrnInfoRec initialisations. Don't allocate any new data
   structures.

   This function is mandatory.

   NOTE: The xf86DrvMsg() functions cannot be used from the Probe.
static Bool
ZZZProbe(DriverPtr drv, int flags)
{
    Bool foundScreen = FALSE;
    int numDevSections, numUsed;
    GDevPtr *devSections;
    int *usedChips;
    int i;

    /*
     * Find the config file Device sections that match this
     * driver, and return if there are none.
     */
    if ((numDevSections = xf86MatchDevice(ZZZ_DRIVER_NAME,
                                          &devSections)) <= 0) {
        return FALSE;
    }

    /*
     * Since this is a PCI card, "probing" just amounts to checking
     * the PCI data that the server has already collected.  If there
     * is none, return.
     *
     * Although the config file is allowed to override things, it
     * is reasonable to not allow it to override the detection
     * of no PCI video cards.
     *
     * The provided xf86MatchPciInstances() helper takes care of
     * the details.
     */
    /* test if PCI bus present */
    if (xf86GetPciVideoInfo()) {

        numUsed = xf86MatchPciInstances(ZZZ_NAME, PCI_VENDOR_ZZZ,
                            ZZZChipsets, ZZZPciChipsets, devSections,
                            numDevSections, drv, &usedChips);

        for (i = 0; i < numUsed; i++) {
            ScrnInfoPtr pScrn = NULL;
            if ((pScrn = xf86ConfigPciEntity(pScrn, flags, usedChips[i],
                                             ZZZPciChipsets, NULL, NULL,
                                             NULL, NULL, NULL))) {
               /* Allocate a ScrnInfoRec */
               pScrn->driverVersion = VERSION;
               pScrn->driverName    = ZZZ_DRIVER_NAME;
               pScrn->name          = ZZZ_NAME;
               pScrn->Probe         = ZZZProbe;
               pScrn->PreInit       = ZZZPreInit;
               pScrn->ScreenInit    = ZZZScreenInit;
               pScrn->SwitchMode    = ZZZSwitchMode;
               pScrn->AdjustFrame   = ZZZAdjustFrame;
               pScrn->EnterVT       = ZZZEnterVT;
               pScrn->LeaveVT       = ZZZLeaveVT;
               pScrn->FreeScreen    = ZZZFreeScreen;
               pScrn->ValidMode     = ZZZValidMode;
               foundScreen = TRUE;
               /* add screen to entity */
           }
        }
        xfree(usedChips);
    }

#ifdef HAS_ISA_DEVS
    /*
     * If the driver supports ISA hardware, the following block
     * can be included too.
     */
    numUsed = xf86MatchIsaInstances(ZZZ_NAME, ZZZChipsets,
                             ZZZIsaChipsets, drv, ZZZFindIsaDevice,
                             devSections, numDevSections, &usedChips);
    for (i = 0; i < numUsed; i++) {
        ScrnInfoPtr pScrn = NULL;
        if ((pScrn = xf86ConfigIsaEntity(pScrn, flags, usedChips[i],
                                         ZZZIsaChipsets, NULL, NULL, NUL
L,
                                         NULL, NULL))) {
            pScrn->driverVersion = VERSION;
            pScrn->driverName    = ZZZ_DRIVER_NAME;
            pScrn->name          = ZZZ_NAME;
            pScrn->Probe         = ZZZProbe;
            pScrn->PreInit       = ZZZPreInit;
            pScrn->ScreenInit    = ZZZScreenInit;
            pScrn->SwitchMode    = ZZZSwitchMode;
            pScrn->AdjustFrame   = ZZZAdjustFrame;
            pScrn->EnterVT       = ZZZEnterVT;
            pScrn->LeaveVT       = ZZZLeaveVT;
            pScrn->FreeScreen    = ZZZFreeScreen;
            pScrn->ValidMode     = ZZZValidMode;
            foundScreen = TRUE;
        }
    }
    xfree(usedChips);
#endif /* HAS_ISA_DEVS */

    xfree(devSections);
    return foundScreen;

AvailableOptions

   Define the AvailableOptions() function. The purpose of this is
   to return the available driver options back to the -configure
   option, so that an xorg.conf file can be built and the user can
   see which options are available for them to use.

PreInit

   Define the PreInit() function. The purpose of this is to find
   all the information required to determine if the configuration
   is usable, and to initialise those parts of the ScrnInfoRec
   that can be set once at the beginning of the first server
   generation. The information should be found in the least
   intrusive way possible.

   This function is mandatory.

   NOTES:
    1. The PreInit() function is only called once during the life
       of the X server (at the start of the first generation).
    2. Data allocated here must be of the type that persists for
       the life of the X server. This means that data that hooks
       into the ScrnInfoRec's privates field should be allocated
       here, but data that hooks into the ScreenRec's devPrivates
       field should not be allocated here. The driverPrivate field
       should also be allocated here.
    3. Although the ScrnInfoRec has been allocated before this
       function is called, the ScreenRec has not been allocated.
       That means that things requiring it cannot be used in this
       function.
    4. Very little of the ScrnInfoRec has been initialised when
       this function is called. It is important to get the order
       of doing things right in this function.

static Bool
ZZZPreInit(ScrnInfoPtr pScrn, int flags)
{
    /* Fill in the monitor field */
    pScrn->monitor = pScrn->confScreen->monitor;

    /*
     * If using the vgahw module, it will typically be loaded
     * here by calling xf86LoadSubModule(pScrn, "vgahw");
     */

    /*
     * Set the depth/bpp.  Use the globally preferred depth/bpp.  If the
     * driver has special default depth/bpp requirements, the defaults s
hould
     * be specified here explicitly.
     * We support both 24bpp and 32bpp framebuffer layouts.
     * This sets pScrn->display also.
     */
    if (!xf86SetDepthBpp(pScrn, 0, 0, 0,
                         Support24bppFb | Support32bppFb)) {
        return FALSE;
    } else {
        if (depth/bpp isn't one we support) {
            print error message;
            return FALSE;
        }
    }
    /* Print out the depth/bpp that was set */
    xf86PrintDepthBpp(pScrn);

    /* Set bits per RGB for 8bpp */
    if (pScrn->depth <= 8) {
        /* Take into account a dac_6_bit option here */
        pScrn->rgbBits = 6 or 8;
    }

    /*
     * xf86SetWeight() and xf86SetDefaultVisual() must be called
     * after pScrn->display is initialised.
     */

    /* Set weight/mask/offset for depth > 8 */
    if (pScrn->depth > 8) {
        if (!xf86SetWeight(pScrn, defaultWeight, defaultMask)) {
            return FALSE;
        } else {
            if (weight isn't one we support) {
                print error message;
                return FALSE;
            }
        }
    }

    /* Set the default visual. */
    if (!xf86SetDefaultVisual(pScrn, -1)) {
        return FALSE;
    } else {
        if (visual isn't one we support) {
            print error message;
            return FALSE;
        }
    }

    /* If the driver supports gamma correction, set the gamma. */
    if (!xf86SetGamma(pScrn, default_gamma)) {
        return FALSE;
    }

    /* This driver uses a programmable clock */
    pScrn->progClock = TRUE;

    /* Allocate the ZZZRec driverPrivate */
    if (!ZZZGetRec(pScrn)) {
        return FALSE;
    }

    pZzz = ZZZPTR(pScrn);

    /* Collect all of the option flags (fill in pScrn->options) */
    xf86CollectOptions(pScrn, NULL);

    /*
     * Process the options based on the information in ZZZOptions.
     * The results are written to pZzz->Options.  If all of the options
     * processing is done within this function a local variable "options
"
     * can be used instead of pZzz->Options.
     */
    if (!(pZzz->Options = xalloc(sizeof(ZZZOptions))))
        return FALSE;
    (void)memcpy(pZzz->Options, ZZZOptions, sizeof(ZZZOptions));
    xf86ProcessOptions(pScrn->scrnIndex, pScrn->options, pZzz->Options);

    /*
     * Set various fields of ScrnInfoRec and/or ZZZRec based on
     * the options found.
     */
    from = X_DEFAULT;
    pZzz->hwCursor = FALSE;
    if (xf86IsOptionSet(pZzz->Options, OPTION_HW_CURSOR)) {
        from = X_CONFIG;
        pZzz->hwCursor = TRUE;
    }
    xf86DrvMsg(pScrn->scrnIndex, from, "Using %s cursor\n",
               pZzz->hwCursor ? "HW" : "SW");
    if (xf86IsOptionSet(pZzz->Options, OPTION_NOACCEL)) {
        pZzz->noAccel = TRUE;
        xf86DrvMsg(pScrn->scrnIndex, X_CONFIG,
                   "Acceleration disabled\n");
    } else {
        pZzz->noAccel = FALSE;
    }
    if (xf86IsOptionSet(pZzz->Options, OPTION_PCI_RETRY)) {
        pZzz->UsePCIRetry = TRUE;
        xf86DrvMsg(pScrn->scrnIndex, X_CONFIG, "PCI retry enabled\n");
    }
    pZzz->fooHack = 0;
    if (xf86GetOptValInteger(pZzz->Options, OPTION_FOO_HACK,
                             &pZzz->fooHack)) {
        xf86DrvMsg(pScrn->scrnIndex, X_CONFIG, "Foo Hack set to %d\n",
                   pZzz->fooHack);
    }

    /*
     * Find the PCI slot(s) that this screen claimed in the probe.
     * In this case, exactly one is expected, so complain otherwise.
     * Note in this case we're not interested in the card types so
     * that parameter is set to NULL.
     */
    if ((i = xf86GetPciInfoForScreen(pScrn->scrnIndex, &pciList, NULL))
        != 1) {
        print error message;
        ZZZFreeRec(pScrn);
        if (i > 0)
            xfree(pciList);
        return FALSE;
    }
    /* Note that pciList should be freed below when no longer needed */

    /*
     * Determine the chipset, allowing config file chipset and
     * chipid values to override the probed information.  The config
     * chipset value has precedence over its chipid value if both
     * are present.
     *
     * It isn't necessary to fill in pScrn->chipset if the driver
     * keeps track of the chipset in its ZZZRec.
     */

    ...

    /*
     * Determine video memory, fb base address, I/O addresses, etc,
     * allowing the config file to override probed values.
     *
     * Set the appropriate pScrn fields (videoRam is probably the
     * most important one that other code might require), and
     * print out the settings.
     */

    ...

    /* Initialise a clockRanges list. */

    ...

    /* Set any other chipset specific things in the ZZZRec */

    ...

    /* Select valid modes from those available */

    i = xf86ValidateModes(pScrn, pScrn->monitor->Modes,
                          pScrn->display->modes, clockRanges,
                          NULL, minPitch, maxPitch, rounding,
                          minHeight, maxHeight,
                          pScrn->display->virtualX,
                          pScrn->display->virtualY,
                          pScrn->videoRam * 1024,
                          LOOKUP_BEST_REFRESH);
    if (i == -1) {
        ZZZFreeRec(pScrn);
        return FALSE;
    }

    /* Prune the modes marked as invalid */

    xf86PruneDriverModes(pScrn);

    /* If no valid modes, return */

    if (i == 0 || pScrn->modes == NULL) {
        print error message;
        ZZZFreeRec(pScrn);
        return FALSE;
    }

    /*
     * Initialise the CRTC fields for the modes.  This driver expects
     * vertical values to be halved for interlaced modes.
     */
    xf86SetCrtcForModes(pScrn, INTERLACE_HALVE_V);

    /* Set the current mode to the first in the list. */
    pScrn->currentMode = pScrn->modes;

    /* Print the list of modes being used. */
    xf86PrintModes(pScrn);

    /* Set the DPI */
    xf86SetDpi(pScrn, 0, 0);

    /* Load bpp-specific modules */
    switch (pScrn->bitsPerPixel) {
    case 1:
        mod = "xf1bpp";
        break;
    case 4:
        mod = "xf4bpp";
        break;
    case 8:
        mod = "cfb";
        break;
    case 16:
        mod = "cfb16";
        break;
    case 24:
        mod = "cfb24";
        break;
    case 32:
        mod = "cfb32";
        break;
    }
    if (mod && !xf86LoadSubModule(pScrn, mod))
        ZZZFreeRec(pScrn);
        return FALSE;


    /* Done */
    return TRUE;
}

MapMem, UnmapMem

   Define functions to map and unmap the video memory and any
   other memory apertures required. These functions are not
   mandatory, but it is often useful to have such functions.
static Bool
ZZZMapMem(ScrnInfoPtr pScrn)
{
    /* Call xf86MapPciMem() to map each PCI memory area */
    ...
    return TRUE or FALSE;
}

static Bool
ZZZUnmapMem(ScrnInfoPtr pScrn)
{
    /* Call xf86UnMapVidMem() to unmap each memory area */
    ...
    return TRUE or FALSE;
}

Save, Restore

   Define functions to save and restore the original video state.
   These functions are not mandatory, but are often useful.
static void
ZZZSave(ScrnInfoPtr pScrn)
{
    /*
     * Save state into per-screen data structures.
     * If using the vgahw module, vgaHWSave will typically be
     * called here.
     */
    ...
}

static void
ZZZRestore(ScrnInfoPtr pScrn)
{
    /*
     * Restore state from per-screen data structures.
     * If using the vgahw module, vgaHWRestore will typically be
     * called here.
     */
    ...
}

ModeInit

   Define a function to initialise a new video mode. This function
   isn't mandatory, but is often useful.
static Bool
ZZZModeInit(ScrnInfoPtr pScrn, DisplayModePtr mode)
{
    /*
     * Program a video mode.  If using the vgahw module,
     * vgaHWInit and vgaRestore will typically be called here.
     * Once up to the point where there can't be a failure
     * set pScrn->vtSema to TRUE.
     */
    ...
}

ScreenInit

   Define the ScreenInit() function. This is called at the start
   of each server generation, and should fill in as much of the
   ScreenRec as possible as well as any other data that is
   initialised once per generation. It should initialise the
   framebuffer layers it is using, and initialise the initial
   video mode.

   This function is mandatory.

   NOTE: The ScreenRec (pScreen) is passed to this driver, but it
   and the ScrnInfoRecs are not yet hooked into each other. This
   means that in this function, and functions it calls, one cannot
   be found from the other.
static Bool
ZZZScreenInit(ScreenPtr pScreen, int argc, char **argv)
{
    /* Get the ScrnInfoRec */
    pScrn = xf86ScreenToScrn(pScreen);

    /*
     * If using the vgahw module, its data structures and related
     * things are typically initialised/mapped here.
     */

    /* Save the current video state */
    ZZZSave(pScrn);

    /* Initialise the first mode */
    ZZZModeInit(pScrn, pScrn->currentMode);

    /* Set the viewport if supported */

    ZZZAdjustFrame(pScrn, pScrn->frameX0, pScrn->frameY0);

    /*
     * Setup the screen's visuals, and initialise the framebuffer
     * code.
     */

    /* Reset the visual list */
    miClearVisualTypes();

    /*
     * Setup the visuals supported.  This driver only supports
     * TrueColor for bpp > 8, so the default set of visuals isn't
     * acceptable.  To deal with this, call miSetVisualTypes with
     * the appropriate visual mask.
     */

    if (pScrn->bitsPerPixel > 8) {
        if (!miSetVisualTypes(pScrn->depth, TrueColorMask,
                              pScrn->rgbBits, pScrn->defaultVisual))
            return FALSE;
    } else {
        if (!miSetVisualTypes(pScrn->depth,
                              miGetDefaultVisualMask(pScrn->depth),
                              pScrn->rgbBits, pScrn->defaultVisual))
            return FALSE;
    }

    /*
     * Initialise the framebuffer.
     */

    switch (pScrn->bitsPerPixel) {
    case 1:
        ret = xf1bppScreenInit(pScreen, FbBase,
                               pScrn->virtualX, pScrn->virtualY,
                               pScrn->xDpi, pScrn->yDpi,
                               pScrn->displayWidth);
        break;
    case 4:
        ret = xf4bppScreenInit(pScreen, FbBase,
                               pScrn->virtualX, pScrn->virtualY,
                               pScrn->xDpi, pScrn->yDpi,
                               pScrn->displayWidth);
        break;
    case 8:
        ret = cfbScreenInit(pScreen, FbBase,
                            pScrn->virtualX, pScrn->virtualY,
                            pScrn->xDpi, pScrn->yDpi,
                            pScrn->displayWidth);
        break;
    case 16:
        ret = cfb16ScreenInit(pScreen, FbBase,
                              pScrn->virtualX, pScrn->virtualY,
                              pScrn->xDpi, pScrn->yDpi,
                              pScrn->displayWidth);
        break;
    case 24:
        ret = cfb24ScreenInit(pScreen, FbBase,
                              pScrn->virtualX, pScrn->virtualY,
                              pScrn->xDpi, pScrn->yDpi,
                              pScrn->displayWidth);
        break;
    case 32:
        ret = cfb32ScreenInit(pScreen, FbBase,
                              pScrn->virtualX, pScrn->virtualY,
                              pScrn->xDpi, pScrn->yDpi,
                              pScrn->displayWidth);
        break;
    default:
        print a message about an internal error;
        ret = FALSE;
        break;
    }

    if (!ret)
        return FALSE;

    /* Override the default mask/offset settings */
    if (pScrn->bitsPerPixel > 8) {
        for (i = 0, visual = pScreen->visuals;
             i < pScreen->numVisuals; i++, visual++) {
            if ((visual->class | DynamicClass) == DirectColor) {
                visual->offsetRed = pScrn->offset.red;
                visual->offsetGreen = pScrn->offset.green;
                visual->offsetBlue = pScrn->offset.blue;
                visual->redMask = pScrn->mask.red;
                visual->greenMask = pScrn->mask.green;
                visual->blueMask = pScrn->mask.blue;
            }
        }
    }

    /*
     * If banking is needed, initialise an miBankInfoRec (defined in
     * "mibank.h"), and call miInitializeBanking().
     */
    if (!miInitializeBanking(pScreen, pScrn->virtualX, pScrn->virtualY,
                                     pScrn->displayWidth, pBankInfo))
        return FALSE;

    /*
     * Set initial black & white colourmap indices.
     */
    xf86SetBlackWhitePixels(pScreen);

    /*
     * Install colourmap functions.
     */

    ...

    /*
     * Initialise cursor functions.  This example is for the mi
     * software cursor.
     */
    miDCInitialize(pScreen, xf86GetPointerScreenFuncs());

    /* Initialise the default colourmap */
    switch (pScrn->depth) {
    case 1:
        if (!xf1bppCreateDefColormap(pScreen))
            return FALSE;
        break;
    case 4:
        if (!xf4bppCreateDefColormap(pScreen))
            return FALSE;
        break;
    default:
        if (!cfbCreateDefColormap(pScreen))
            return FALSE;
        break;
    }

    /*
     * Wrap the CloseScreen vector and set SaveScreen.
     */
    ZZZPTR(pScrn)->CloseScreen = pScreen->CloseScreen;
    pScreen->CloseScreen = ZZZCloseScreen;
    pScreen->SaveScreen = ZZZSaveScreen;

    /* Report any unused options (only for the first generation) */
    if (serverGeneration == 1) {
        xf86ShowUnusedOptions(pScrn->scrnIndex, pScrn->options);
    }

    /* Done */
    return TRUE;
}

SwitchMode

   Define the SwitchMode() function if mode switching is supported
   by the driver.
static Bool
ZZZSwitchMode(ScrnInfoPtr pScrn, DisplayModePtr mode)
{
    return ZZZModeInit(pScrn, mode);
}

AdjustFrame

   Define the AdjustFrame() function if the driver supports this.
static void
ZZZAdjustFrame(ScrnInfoPtr pScrn, int x, int y)
{
    /* Adjust the viewport */
}

EnterVT, LeaveVT

   Define the EnterVT() and LeaveVT() functions.

   These functions are mandatory.
static Bool
ZZZEnterVT(ScrnInfoPtr pScrn)
{
    return ZZZModeInit(pScrn, pScrn->currentMode);
}

static void
ZZZLeaveVT(ScrnInfoPtr pScrn)
{
    ZZZRestore(pScrn);
}

CloseScreen

   Define the CloseScreen() function:

   This function is mandatory. Note that it unwraps the previously
   wrapped pScreen->CloseScreen, and finishes by calling it.
static Bool
ZZZCloseScreen(ScreenPtr pScreen)
{
    ScrnInfoPtr pScrn = xf86ScreenToScrn(pScreen);
    if (pScrn->vtSema) {
        ZZZRestore(pScrn);
        ZZZUnmapMem(pScrn);
    }
    pScrn->vtSema = FALSE;
    pScreen->CloseScreen = ZZZPTR(pScrn)->CloseScreen;
    return (*pScreen->CloseScreen)(pScreen);
}

SaveScreen

   Define the SaveScreen() function (the screen blanking
   function). When using the vgahw module, this will typically be:
static Bool
ZZZSaveScreen(ScreenPtr pScreen, int mode)
{
    return vgaHWSaveScreen(pScreen, mode);
}

   This function is mandatory. Before modifying any hardware
   register directly this function needs to make sure that the
   Xserver is active by checking if pScrn is non-NULL and for
   pScrn->vtSema == TRUE.

FreeScreen

   Define the FreeScreen() function. This function is optional. It
   should be defined if the ScrnInfoRec driverPrivate field is
   used so that it can be freed when a screen is deleted by the
   common layer for reasons possibly beyond the driver's control.
   This function is not used in during normal (error free)
   operation. The per-generation data is freed by the
   CloseScreen() function.
static void
ZZZFreeScreen(ScrnInfoPtr pScrn)
{
    /*
     * If the vgahw module is used vgaHWFreeHWRec() would be called
     * here.
     */
    ZZZFreeRec(pScrn);
}
