Re: [PATCH 2/3] ASoC: core: Inline resume work back to resume function

[Cezary Rojewski <cezary.rojewski@intel.com>]

On 2022-11-07 3:28 PM, Mark Brown wrote:

> It'd be good to at least have some idea of practical usage as well, the
> functions return void because nothing was making any use of the return
> values.

The problem is mainly connected to a resume operation as even if 
something fails at suspend, there is a chance for the driver to recover 
things up during resume.

Now, if something fails during the resume operation, blindly returning 0 
makes userspace think everything is fine and we can keep going, whereas 
the stream may no longer be operational and requires complete recovery 
(close, reopen).

alsa-utils/aplay/aplay.c does snd_pcm_resume() as long as -EAGAIN is 
returned, then falls back to snd_pcm_prepare() before finally giving up. 
As snd_pcm_prepare() checks pcm's state before invoking ->prepare(), one 
option is to set substream->runtime->status->state to 
SNDRV_PCM_STATE_DISCONNECTED to ensure dai->hw_free() gets called right 
after.

TLDR: it all comes down to some granularity missing. Suspend/resume for 
the AudioDSP drivers do basically entire pcm-lifecycle within what is 
supposed to be a simple TRIGGER_SUSPEND/RESUME operation.

> There's also an expectation that suspend and resume be fast...

You're right. Sound devices should not disturb the PM for the entire system.

Looking at this after thinking the performance/stability argument 
through, indeed deferring work is a good way of dealing with the situation.


Regards,
Czarek