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 21.1.18

2025-06-18

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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-21.1.18
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 21.1.18 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       Specifies the name of the driver to be used for the card. This is
"drivername" mandatory.

             Specifies uniquely the location of the card on the bus. The
             purpose is to identify particular cards in a multi-headed
BusID        configuration. The format of the argument is intentionally vague,
"busslot"    and may be architecture dependent. For a PCI bus, it is something
             like "bus@domain:slot:func". The "@domain" part can be left out
             for domain 0.

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 the origin of the physical view port.
change

ScreenSaver    Screen saver activation/deactivation.
state change

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.

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

The VidMode extension also requires:

          Identify if a new mode is usable with the current configuration. The
ValidMode 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
shareable. 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 (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 (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.

        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 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 shareable 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.

        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
          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
          memBase
          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 shareable 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:

            • enable port I/O access

            • save and initialise the bus/resource state

            • enter the SETUP server state

            • calls ChipEnterVT() for each screen
On ENTER:
            • enter the OPERATING server state

            • validate GCs

            • Restore fb from saved pixmap for each screen

            • Enable all input devices

            • Save fb to pixmap for each screen

            • validate GCs

            • enter the SETUP server state

On LEAVE:   • 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, NewApertureAddress);


        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 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.

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.

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 shareable 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 shareable 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 *PCIchipsets,
                                  GDevPtr *devList, int numDevs, DriverPtr drvp,
                                  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.

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 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.

Two helper functions are provided to aid configuring entities:

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



        This functions is used to register the entity. The res, init, enter,
        and leave arguments are unused, and should be NULL. For active entities
        a ScrnInfoRec is allocated if the pScrn argument is NULL. The return
        value is TRUE when successful.

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

        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.

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.

        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 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.

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 *name);


        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 *name);


        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, Bool 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 loadPalette,
                                 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):

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

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

                                    reload the colormap even if the screen is
                                    switched out of the server's VC. The
        CMAP_LOAD_EVEN_IF_OFFSCREEN 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.

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

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

                     DGA_FILL_RECT         Indicates that the driver supports
                     DGA_BLIT_RECT         the FillRect, BlitRect or
                     DGA_BLIT_RECT_TRANS   BlitTransRect functions in this
    flags                                  mode.

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

                     DGA_INTERLACED        Indicates that these are interlaced
                     DGA_DOUBLESCAN        or double scan modes.

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

    pixmapWidth      These are the dimensions of the area of the framebuffer
    pixmapHeight     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,      The RGB masks for this mode, if applicable.
    blue_mask

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

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

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

                     The following may be OR'd together:

                     DGA_FLIP_IMMEDIATE The driver supports immediate viewport
    viewportFlags                       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.

                   The name of the device to open or NULL if there is no
            name   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.

                               The viewport change should occur at the vertical
            DGA_FLIP_RETRACE   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:

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

                                      These refer to the target drawable and
                                      are similar to a Window's class.
                         XvInputMask  XvInputMask indicates that the adaptor
                         XvOutputMask can put video into a drawable.
                                      XvOutputMask indicates that the adaptor
                                      can get video from a drawable.
type
                         XvVideoMask  These indicate that the adaptor supports
                         XvStillMask  video, still or image primitives
                         XvImageMask  respectively.

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

                         Currently, the following flags are defined:

                                                Implementing PutStill for
                                                hardware that does video as an
                                                overlay can be awkward since
                                                it's unclear how long to leave
                         VIDEO_OVERLAID_STILLS  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
flags                                           then.

                         VIDEO_OVERLAID_IMAGES  Same as VIDEO_OVERLAID_STILLS
                                                but for images.

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

name                     The name of the adaptor.

                         The number of encodings the adaptor is capable of and
                         pointer to the XF86VideoEncodingRec array. The 
                         XF86VideoEncodingRec is described later on. For
nEncodings pEncodings    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.

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

                         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
nPorts pPortPrivates     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.

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

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

                         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
PutVideo PutStill            adaptor type does not contain XvVideoMask.
GetVideo GetStill
StopVideo                 4. GetStill and PutStill are not required when the
SetPortAttribute             adaptor type does not contain XvStillMask.
GetPortAttribute
QueryBestSize PutImage    5. PutImage and QueryImageAttributes are not required
QueryImageAttributes         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 data);


        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:

                        This is a unique descriptor for the format. It is often
        id              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.

                        The number of bits taken up (but not necessarily used)
        bits_per_pixel  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
                        (analogous to the depth of a pixmap format).

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

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

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

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

                        Uppercase ascii characters representing the order that
                        samples are stored within packed formats. For planar
        component_order 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, pointer options,
                           const XF86ModReqInfo * modreq, int *errmaj);


        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:

                An optional parameter that is passed to the newly loaded
                module's SetupProc function (if it has one). This argument is
        options 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.

                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;
                        CARD8        minorversion;
                        CARD16       patchlevel;
                        const char * abiclass;
                        CARD32       abiversion;
                        const char * moduleclass;
                } XF86ModReqInfo;


                The information here is compared against the equivalent
        modreq  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.

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

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

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

        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 tool */
    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:

             The module's name. This field is currently only for informational
modname      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.

             This field holds the first part of a signature that can be used to
_modinfo1_   locate this structure in the binary. It should always be
             initialised to MODINFOSTRING1.

             This field holds the second part of a signature that can be used
_modinfo2_   to locate this structure in the binary. It should always be
             initialised to MODINFOSTRING2.

             The XFree86 version against which the module was compiled. This is
xf86version  mostly for informational/diagnostic purposes. It should be
             initialised to XF86_VERSION_CURRENT, which is defined in
             xf86Version.h.

             The module-specific major version. For modules where this version
majorversion 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.

             The module-specific minor version. For modules where this version
             is used for more than simply informational purposes, the minor
minorversion 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.

             The module-specific patch level. The patch level should increase
patchlevel   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.

             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
abiclass
             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

             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:
abiversion

                                ABI_ANSIC_VERSION
                                ABI_VIDEODRV_VERSION
                                ABI_XINPUT_VERSION
                                ABI_EXTENSION_VERSION
               

             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:
moduleclass

                                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 **patternlist,
                              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.

        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[], int size, Bool builtin);


        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.

                     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

        depth24flags 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.

        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.

                     A list of clock ranges allowed by the driver. Each range
        clockRanges  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.

                     Minimum line pitch supported by the driver. This must be
        minPitch     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.

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

                     If greater than zero, this is the virtual height value
        virtualY     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.

                     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
        strategy     one of the above:

                     LOOKUP_CLKDIV2             Allow halved clocks

                                                Allow missing horizontal sync
                     LOOKUP_OPTIONAL_TOLERANCES 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)

        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.

                     One mode entry for each of the requested modes, with the
        modes        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.

        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:

                          The lower and upper mode clock bounds for which the
                          rest of the clockRange parameters apply. Since these
        minClock,         are the mode clocks, they are not scaled with the
        maxClock          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

                          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
        ClockMulFactor,   to the mode clock to achieve the data transport clock
        ClockDivFactor    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.

                          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
        PrivFlags         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      initialised with the default overscan index
        [0x11]

        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 numAttribute);


        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);
    }

    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 should
     * 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);
}



