drm/i915: Force CPU synchronisation even if userspace requests ASYNC
The goal here was to minimise doing any thing or any check inside the kernel that was not strictly required. For a userspace that assumes complete control over the cache domains, the kernel is usually using outdated information and may trigger clflushes where none were required. However, swapping is a situation where userspace has no knowledge of the domain transfer, and will leave the object in the CPU cache. The kernel must flush this out to the backing storage prior to use with the GPU. As we use an asynchronous task tracked by an implicit fence for this, we also need to cancel the ASYNC flag on the object so that the object will wait for the clflush to complete before being executed. This also absolves userspace of the responsibility imposed by commit 77ae9957 ("drm/i915: Enable userspace to opt-out of implicit fencing") that its needed to ensure that the object was out of the CPU cache prior to use on the GPU. Fixes: 77ae9957 ("drm/i915: Enable userspace to opt-out of implicit fencing") Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=101571Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Cc: Jason Ekstrand <jason@jlekstrand.net> Reviewed-by: Jason Ekstrand <jason@jlekstrand.net> Link: https://patchwork.freedesktop.org/patch/msgid/20170721145037.25105-5-chris@chris-wilson.co.ukReviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
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