On ti, 2017-02-14 at 20:17 -0800, Kenneth Graunke wrote: > This patch makes the I915_PARAM_HAS_EXEC_CONSTANTS getparam return 0 > (indicating the optional feature is not supported), and makes execbuf > always return -EINVAL if the flags are used. > > Apparently, no userspace ever shipped which used this optional feature: > I checked the git history of Mesa, xf86-video-intel, libva, and Beignet, > and there were zero commits showing a use of these flags. Kernel commit > 72bfa19c8deb4 apparently introduced the feature prematurely. > > 'relative_constants_mode' has always been tracked per-device, but this > has actually been wrong ever since hardware contexts were introduced, as > the INSTPM register is saved (and automatically restored) as part of the > render ring context. The software per-device value could therefore get > out of sync with the hardware per-context value. This meant that using > them is actually unsafe: a client which tried to use them could damage > the state of other clients, causing the GPU to interpret their BO > offsets as absolute pointers, leading to bogus memory reads. > > These flags were also never ported to execlist mode, making them no-ops > on Gen9+ (which requires execlists), and Gen8 in the default mode. > > On Gen8+, userspace can write these registers directly, achieving the > same effect. On Gen6-7.5, it likely makes sense to extend the command > parser to support them. I don't think anyone wants this on Gen4-5. > > Based on a patch by Dave Gordon. > > Cc: Dave Gordon <david.s.gordon@xxxxxxxxx> > Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=92448 > Signed-off-by: Kenneth Graunke <kenneth@xxxxxxxxxxxxx> Explanation makes sense, only Google hits seem to be on Mesa detecting the feature and later, removing the detection when unused. Reviewed-by: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx> Regards, Joonas -- Joonas Lahtinen Open Source Technology Center Intel Corporation _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
