[Intel-gfx] [PATCH] drm/i915/execlists: Clear STOP_RING bit before restoring the context

[Chris Wilson]

Quoting Chris Wilson (2018-08-14 14:11:50)
> Before a reset, we set the STOP_RING bit of RING_MI_MODE to freeze the
> engine. However, sometimes we observe that upon restart, the engine
> freezes again with the STOP_RING bit still asserted. By inspection, we
> know that the register itself is cleared by the GPU reset, so that bit
> must be preserved inside the context image and reloaded from there. A
> simple fix (as the RING_MI_MODE is at a fixed offset in a valid context)
> is to clobber the STOP_RING bit inside the image before replaying the
> request.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> Cc: Michel Thierry <michel.thierry at intel.com>
> Cc: Michał Winiarski <michal.winiarski at intel.com>

Note that we need to improve the active request tracking before this is
100% reliable. One patch at a time; though you can look at the
i915_reset.c restructuring series to see what I have in mind.
-Chris