As another precaution when testing whether the CS engine is actually
idle, also inspect the ring's HEAD/TAIL registers, which should be equal
when there are no commands left to execute by the GPU.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170530121334.17364-3-chris@chris-wilson.co.ukReviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>