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authormarha <marha@users.sourceforge.net>2011-05-16 08:06:12 +0000
committermarha <marha@users.sourceforge.net>2011-05-16 08:06:12 +0000
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xserver xkeyboar-config mesa git update 16 May 2011
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+Adding EXA support to your X.Org video driver
+---------------------------------------------
+EXA (for EXcellent Architecture or Ex-kaa aXeleration Architecture or
+whatever) aims to extend the life of the venerable XFree86 video drivers by
+introducing a new set of acceleration hooks that efficiently accelerate the X
+Render extension, including solid fills, blits within screen memory and to and
+from system memory, and Porter-Duff compositing and transform operations.
+
+Configuration
+-------------
+A new config file option, AccelMethod, should be added to your driver, to allow
+the user to select between the EXA and XAA acceleration APIs.
+
+Some drivers implement a per-instance useEXA flag to track whether EXA is
+active or not. It can be helpful to also conditionalize XAA support with an
+ifdef so that it can easily be turned off/removed in the future.
+
+Setting the flag and checking for AccelMethod can be done in the driver's
+Options parsing routine.
+
+Loading EXA
+------------
+EXA drivers in the XFree86 DDX should use the loadable module loader to load
+the EXA core. Careful versioning allows the EXA API to be extended without
+breaking the ABI for older versions of drivers. Example code for loading EXA:
+
+static const char *exaSymbols[] = {
+ "exaDriverAlloc",
+ "exaDriverInit",
+ "exaDriverFini",
+ "exaOffscreenAlloc",
+ "exaOffscreenFree",
+ "exaGetPixmapOffset",
+ "exaGetPixmapPitch",
+ "exaGetPixmapSize",
+ "exaMarkSync",
+ "exaWaitSync",
+ NULL
+};
+
+ if (info->useEXA) {
+ info->exaReq.majorversion = 2;
+ info->exaReq.minorversion = 0;
+
+ if (!LoadSubModule(pScrn->module, "exa", NULL, NULL, NULL,
+ &info->exaReq, &errmaj, &errmin)) {
+ LoaderErrorMsg(NULL, "exa", errmaj, errmin);
+ return FALSE;
+ }
+ xf86LoaderReqSymLists(exaSymbols, NULL);
+ }
+
+EXA is then initialized using exaDriverAlloc and exaDriverInit. See doxygen
+documentation for getting started there.
+
+Further documentation
+------------
+The EXA driver interface and public API is documented using doxygen in
+xserver/xorg/exa/. To build the documentation, run:
+ doxygen -g
+ doxygen Doxyfile
+The resulting documentation will appear an html/index.html under the current
+directory.
+
+EXA initialization
+------------------
+Your driver's AccelInit routine must initialize an ExaDriverRec structure if
+EXA support is enabled, with appropriate error handling (i.e. NoAccel and
+NoXvideo should be set to true if EXA fails to initialize for whatever
+reason).
+
+The AccelInit routine also needs to make sure that there's enough offscreen
+memory for certain operations to function, like Xvideo, which should advertise
+a maximum size no larger than can be dealt with given the amount of offscreen
+memory available.
+
+EXA and Xv
+----------
+Video support becomes easier with EXA since AllocateFBMemory can use
+exaOffscreenAlloc directly, freeing a previous area if necessary and
+allocating a new one. Likewise, FreeFBMemory can call exaOffscreenFree.
+
+EXA teardown
+------------
+At screen close time, EXA drivers should call exaDriverFini with their screen
+pointer, free their EXADriver structure, and do any other necessary teardown.
+
+EXA misc.
+---------
+In many drivers, DGA support will need to be changed to be aware of the new
+EXA support.
+
+Send updates and corrections to Jesse Barnes <jbarnes@virtuousgeek.org> or
+just check them in if you have permission.