[Intel-gfx] [PATCH 3/3] snd/hda: Protect concurrent display_power_status with a mutex

[Chris Wilson]

Quoting Takashi Iwai (2019-01-14 17:46:57)
> On Mon, 14 Jan 2019 18:37:53 +0100,
> Chris Wilson wrote:
> > 
> > Just in case the audio linkage is swapped between components during the
> > runtime pm sequence, we need to protect the rpm tracking with a mutex.
> 
> It's not clear to me how does this happens.
> Could you elaborate a bit more the scenario?

The code is written such that multiple bits within display_power_status
can be set and cleared simultaneously. There was no serialisation
mentioned in the routine, so I was fearful that the display_power_active
here was being accessed concurrently -- and if that was explaining why
snd/hda appears to be leaking the runtime pm (or at least is holding on
to the wakeref longer than igt expects, > 10s).
-Chris