[Intel-gfx] [PATCH 2/2] drm/i915: Force reset on unready engine

[Chris Wilson]

Quoting Mika Kuoppala (2018-08-13 11:42:42)
> If engine reports that it is not ready for reset, we
> give up. Evidence shows that forcing a per engine reset
> on an engine which is not reporting to be ready for reset,
> can bring it back into a working order. There is risk that
> we corrupt the context image currently executing on that
> engine. But that is a risk worth taking as if we unblock
> the engine, we prevent a whole device wedging in a case
> of full gpu reset.
> 
> Reset individual engine even if it reports that it is not
> prepared for reset, but only if we aim for full gpu reset
> and not on first reset attempt.
> 
> v2: force reset only on later attempts, readability (Chris)
> v3: simplify with adequate caffeine levels (Chris)
> 
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Signed-off-by: Mika Kuoppala <mika.kuoppala at linux.intel.com>
Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>

One last thing, you said you recalled one of the reasons for its
existence was to prevent machine lockups on kbl. Is the recollection
true? Do we want to leave a comment in case of fire?
-Chris