drm/i915/execlists: Reset the CSB head tracking on reset/sanitization
We can avoid the mmio read of the CSB pointers after reset based on the knowledge that the HW always start writing at entry 0 in the CSB buffer. We need to reset our CSB head tracking after GPU reset (and on sanitization after resume) so that we are expecting to read from entry 0, hence we reset our head tracking back to the entry before (the last entry in the ring). Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20180615093137.14270-2-chris@chris-wilson.co.uk
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