95 lines
3.3 KiB
Plaintext
95 lines
3.3 KiB
Plaintext
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Adding EXA support to your X.Org video driver
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---------------------------------------------
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EXA (for EXcellent Architecture or Ex-kaa aXeleration Architecture or
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whatever) aims to extend the life of the venerable XFree86 video drivers by
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introducing a new set of acceleration hooks that efficiently accelerate the X
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Render extension, including solid fills, blits within screen memory and to and
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from system memory, and Porter-Duff compositing and transform operations.
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Configuration
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-------------
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A new config file option, AccelMethod, should be added to your driver, to allow
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the user to select between the EXA and XAA acceleration APIs.
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Some drivers implement a per-instance useEXA flag to track whether EXA is
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active or not. It can be helpful to also conditionalize XAA support with an
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ifdef so that it can easily be turned off/removed in the future.
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Setting the flag and checking for AccelMethod can be done in the driver's
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Options parsing routine.
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Loading EXA
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------------
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EXA drivers in the XFree86 DDX should use the loadable module loader to load
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the EXA core. Careful versioning allows the EXA API to be extended without
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breaking the ABI for older versions of drivers. Example code for loading EXA:
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static const char *exaSymbols[] = {
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"exaDriverAlloc",
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"exaDriverInit",
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"exaDriverFini",
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"exaOffscreenAlloc",
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"exaOffscreenFree",
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"exaGetPixmapOffset",
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"exaGetPixmapPitch",
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"exaGetPixmapSize",
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"exaMarkSync",
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"exaWaitSync",
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NULL
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};
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if (info->useEXA) {
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info->exaReq.majorversion = 2;
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info->exaReq.minorversion = 0;
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if (!LoadSubModule(pScrn->module, "exa", NULL, NULL, NULL,
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&info->exaReq, &errmaj, &errmin)) {
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LoaderErrorMsg(NULL, "exa", errmaj, errmin);
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return FALSE;
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}
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xf86LoaderReqSymLists(exaSymbols, NULL);
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}
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EXA is then initialized using exaDriverAlloc and exaDriverInit. See doxygen
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documentation for getting started there.
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Further documentation
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------------
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The EXA driver interface and public API is documented using doxygen in
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xserver/xorg/exa/. To build the documentation, run:
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doxygen -g
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doxygen Doxyfile
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The resulting documentation will appear an html/index.html under the current
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directory.
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EXA initialization
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------------------
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Your driver's AccelInit routine must initialize an ExaDriverRec structure if
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EXA support is enabled, with appropriate error handling (i.e. NoAccel and
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NoXvideo should be set to true if EXA fails to initialize for whatever
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reason).
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The AccelInit routine also needs to make sure that there's enough offscreen
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memory for certain operations to function, like Xvideo, which should advertise
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a maximum size no larger than can be dealt with given the amount of offscreen
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memory available.
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EXA and Xv
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----------
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Video support becomes easier with EXA since AllocateFBMemory can use
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exaOffscreenAlloc directly, freeing a previous area if necessary and
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allocating a new one. Likewise, FreeFBMemory can call exaOffscreenFree.
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EXA teardown
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------------
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At screen close time, EXA drivers should call exaDriverFini with their screen
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pointer, free their EXADriver structure, and do any other necessary teardown.
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EXA misc.
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---------
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In many drivers, DGA support will need to be changed to be aware of the new
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EXA support.
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Send updates and corrections to Jesse Barnes <jbarnes@virtuousgeek.org> or
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just check them in if you have permission.
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