Re: S4 resume breakage with i915 driver

[Imre Deak <imre.deak@intel.com>]

On pe, 2016-08-26 at 11:39 +0100, Chris Wilson wrote:
> On Fri, Aug 26, 2016 at 12:25:01PM +0200, Takashi Iwai wrote:
> > On Fri, 26 Aug 2016 11:18:00 +0200,
> > Takashi Iwai wrote:
> > > I had to modify the intel_gpu_reset() call because the test was done
> > > on the older kernel, so it's like:
> > > 
> > > +       intel_gpu_reset(dev_to_i915(dev)->dev);
> > > 
> > > And, it seems working on HSW! \o/
> > > 
> > > A simple trick, better than the magical register write revert.
> > > I'll check other machines, too, to see whether it has any negative
> > > impact.
> > 
> > The test results look good on all machines.
> 
> The theory then is that the GPU's are active across the load of the
> hibernation image and so before the GTT is updated the memory currently
> in use by the GPU is reused by the system.
> 
> The key question then is the memory of boot kernel still in place during
> the hibernate restore phase?

Before restoring the image all devices are quiesced by calling their
freeze callback, so the GPU should be idle already
in i915_pm_restore_early() already.

> If we need to add a ->shutdown callback (if
> that is even called before hibernate restore) then we can only fix
> future kernels and are still susceptible to corruption when booing from
> old kernels.
> 
> Any one familiar with the details of the hibernation restore? (And how
> much relates to kexec?)
> -Chris
> 
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