drivers/gpu/drm/i915/i915_gem_execbuffer.c · 954ce087072cceb25a9106ba85d98e3219e4af7a · Kirill Smelkov / linux

commit upstream. 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 apparently introduced the feature prematurely. According to Chris, the intention was to use this in cairo-drm, but "the use was broken for gen6", so I don't think it ever happened. '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. v3: Return -ENODEV for the getparam, as this is what we do for other obsolete features. Suggested by Chris Wilson. Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=92448Signed-off-by: