[Intel-gfx] [PATCH 2/3] drm/i915: Prefer checking the wakeref itself rather than the counter

[Chris Wilson]

Quoting Chris Wilson (2019-05-01 14:57:52)
> The counter goes to zero at the start of the parking cycle, but the
> wakeref itself is held until the end. Likewise, the counter becomes one
> at the end of the unparking, but the wakeref is taken first. If we check
> the wakeref instead of the counter, we include the unpark/unparking time
> as intel_wakeref_is_active(), and do not spuriously declare inactive if
> we fail to park (i.e. the parking and wakeref drop is postponed).
> 
> The premature inactive deactivation may result us in randomly stopping
> the retire worker too early with a potential for a livelock if that was
> the only means by which we were retiring at the time (e.g. in handling
> i915_drop_caches).

Forget this paragraph, this was not the solution. I need the longer active
boundary for the next patch.
-Chris