drm/i915/execlists: Reinitialise context image after GPU hang
On Braswell, at least, we observe that the context image is written in multiple phases. The first phase is to clear the register state, and subsequently rewrite it. A GPU reset at the right moment can interrupt the context update leaving it corrupt, and our update of the RING_HEAD is not sufficient to restart the engine afterwards. To recover, we need to reset the registers back to their original values. The context state is lost. What we need is a better mechanism to serialise the reset with pending flushes from the GPU. Fixes: 821ed7df ("drm/i915: Update reset path to fix incomplete requests") Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk> Cc: Mika Kuoppala <mika.kuoppala@intel.com> Reviewed-by: NMika Kuoppala <mika.kuoppala@intel.com> Link: http://patchwork.freedesktop.org/patch/msgid/20161004201132.21801-2-chris@chris-wilson.co.uk (cherry picked from commit a3aabe86) Signed-off-by: NJani Nikula <jani.nikula@intel.com>
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