[Intel-gfx] [PATCH v2 1/1] drm/i915: Suspend GuC prior to GPU Reset during GEM suspend

[Chris Wilson]

On Wed, Apr 05, 2017 at 03:54:27PM +0300, Joonas Lahtinen wrote:
> On ke, 2017-04-05 at 15:51 +0530, Sagar Arun Kamble wrote:
> > i915 is currently doing Full GPU reset at the end of suspend followed by
> > GuC suspend. This reset bypasses the GuC. We need to tell the GuC to
> > suspend before we do a direct intel_gpu_reset, Otherwise the gpu state will
> > no longer match the GuC's expectations and its suspend will not be
> > successful. With this change, i915 suspends GuC after suspending GEM and
> > before doing Full GPU reset.
> 
> + David, Oscar and Michel
> 
> My understanding is that reloading GuC firmware after each resume is a
> major bottleneck in resume time, and we instead should be telling GuC
> to suspend and not reset the GPU, at most only reset the engines.

resetting the gpu is for robustness, to make sure that the gpu is truly
inactive after we lose control. Now you might argue to move that to only
the hibernate paths, but paranoia says to do it before the bios is
invovled on suspend.

We do not need to wait for firmware to load, on init or resume, along
with most things we can do it asynchronously. We could even start
userspace with execlists and then switch to guc, if firmware loading was
that slow (or just the firmware was non-existent e.g. builtin with no
initrd).
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre