[Intel-gfx] [PATCH 3/5] drm/i915: Add timeline barrier support

[Chris Wilson]

Quoting Tvrtko Ursulin (2019-01-25 15:24:39)
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> Timeline barrier allows serialization between different timelines.
> 
> After calling i915_timeline_set_barrier with a request, all following
> submissions on this timeline will be set up as depending on this request,
> or barrier. Once the barrier has been completed it automatically gets
> cleared and things continue as normal.
> 
> This facility will be used by the upcoming context SSEU code.
> 
> v2:
>  * Assert barrier has been retired on timeline_fini. (Chris Wilson)
>  * Fix mock_timeline.
> 
> v3:
>  * Improved comment language. (Chris Wilson)
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> Suggested-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>

I sent a fix for this yesterday, we need to preserve the earlier barrier
chain setting a new barrier (or else it fails if mix barriers along
different timelines).
-Chris