[Intel-gfx] [PATCH v2 1/2] PCI / PM: Add needs_resume flag to avoid suspend complete optimization

[Imre Deak]

On Tue, Apr 25, 2017 at 08:21:49AM +0200, Lukas Wunner wrote:
> On Mon, Apr 24, 2017 at 10:56:40PM +0200, Rafael J. Wysocki wrote:
> > On Monday, April 24, 2017 10:42:42 PM Lukas Wunner wrote:
> > > On Mon, Apr 24, 2017 at 10:02:30PM +0200, Lukas Wunner wrote:
> > > > On Mon, Apr 24, 2017 at 05:27:42PM +0300, Imre Deak wrote:
> > > > > Some drivers - like i915 - may not support the system suspend direct
> > > > > complete optimization due to differences in their runtime and system
> > > > > suspend sequence. Add a flag that when set resumes the device before
> > > > > calling the driver's system suspend handlers which effectively disables
> > > > > the optimization.
> > > > 
> > > > FWIW, there are at least two alternative solutions to this problem which
> > > > do not require changes to the PCI core:
> > > > 
> > > > (1) Add a ->prepare hook to i915_pm_ops which calls pm_runtime_get_sync()
> > > >     and a ->complete hook which calls pm_runtime_put().
> > > 
> > > Thinking a bit more about this, it's even simpler:  The PM core acquires
> > > a runtime PM ref in device_prepare() and releases it in device_complete(),
> > > so it's sufficient to just call pm_runtime_resume() in a ->prepare hook
> > > that's newly added to i915.  No ->complete hook necessary.  Tentative
> > > patch below, based on drm-intel-fixes, would replace both of your patches.
> > 
> > Calling it in ->prepare() means that everybody is now waiting for you to
> > resume.
> > 
> > Not quite optimal IMO.
> 
> Okay, understood.
> 
> However in the absence of a device_link from the HDA device (consumer)
> to the GPU (supplier), there's no guarantee that the GPU is resumed
> when the HDA device needs it due to the asynchronous invocation of
> the ->suspend hooks.  This is assuming that the HDA device already
> needs the GPU during ->suspend phase.

i915 has ->resume_early and ->suspend_late hooks that provides the above
guarantee.

--Imre