drm/i915/perf: avoid read back of head register
authorRobert Bragg <robert@sixbynine.org>
Thu, 11 May 2017 15:43:26 +0000 (16:43 +0100)
committerChris Wilson <chris@chris-wilson.co.uk>
Sat, 13 May 2017 09:59:39 +0000 (10:59 +0100)
commitf279020a02c187d352d40e0dc33d7439f0fc2cce
treecf8d18fb92512d320d5b7f13d54b8f9f3f281f62
parent26ebd9c734d5b807055c333b29504b05fe971185
drm/i915/perf: avoid read back of head register

There's no need for the driver to keep reading back the head pointer
from hardware since the hardware doesn't update it automatically. This
way we can treat any invalid head pointer value as a software/driver
bug instead of spurious hardware behaviour.

This change is also a small stepping stone towards re-working how
the head and tail state is managed as part of an improved workaround
for the tail register race condition.

Signed-off-by: Robert Bragg <robert@sixbynine.org>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170511154345.962-4-lionel.g.landwerlin@intel.com
drivers/gpu/drm/i915/i915_drv.h
drivers/gpu/drm/i915/i915_perf.c