[Intel-gfx] [PATCH v2 1/2] drm/i915/guc: Fill preempt context once at init time

[Chris Wilson]

Quoting Michał Winiarski (2018-02-26 16:37:59)
> Since we're inhibiting context save of preempt context, we're no longer
> tracking the position of HEAD/TAIL. With GuC, we're adding a new
> breadcrumb for each preemption, which means that the HW will do more and
> more breadcrumb writes. Eventually the ring is filled, and we're
> submitting the preemption context with HEAD==TAIL==0, which won't result
> in breadcrumb write, but will trigger hangcheck instead.
> Instead of writing a new preempt breadcrumb for each preemption, let's
> just fill the ring once at init time (which also saves a couple of
> instructions in the tasklet).
> 
> v2: Assert that context save restore is inhibited, don't assert on ring
>     alignment. (Chris)
> 
> Fixes: 517aaffe0c1b ("drm/i915/execlists: Inhibit context save/restore for the fake preempt context")
> Signed-off-by: Michał Winiarski <michal.winiarski at intel.com>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
> Cc: Michel Thierry <michel.thierry at intel.com>
> Cc: Mika Kuoppala <mika.kuoppala at intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>

And pushed with the minor whitespace cleanup to appease checkpatch.
Thanks for the fix!
-Chris