[PATCH 1/2] drm/i915: Restore GT coarse power gating workaround

[Imre Deak]

On Thu, Dec 19, 2019 at 04:42:44PM +0000, Chris Wilson wrote:
> Quoting Imre Deak (2019-11-14 16:42:24)
> > The workaround to disable coarse power gating is still needed on SKL
> > GT3/GT4 machines and since the RC6 context corruption was discovered by
> > the hardware team also on all GEN9 machines. Restore applying the
> > workaround.
> 
> What exactly is the link between powergating and the rc6 power context
> corruption? Disabling powergating entirely is quite a significant
> regression -- and we can't partially enable powergating for idle engines
> as the HW refuses to cooperate.
> 
> So is it safe to enable powergating if only vcs is busy [rcs is idle]?

The problem with CPG wrt. possible RC6 corruption is that if a
corruption happens on one engine while another is already idle (having
saved its context) then this idle engine won't be able to resume any
more (since it cannot restore its context from the corrupted RC6 state).

> -Chris
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