On Thu, 09 May 2019 18:56:12 +0200, Ranjani Sridharan wrote:
Hm, it's a good question. Currently the PCM core doesn't care about the paused stream wrt PM by the assumption that the paused / stopped stream doesn't need a special resume treatment. But, generally speaking, the pause-release won't work for a hardware that doesn't support the full resume, either. For example, the legacy HD-audio may restart from some wrong position if resumed from the pause.
Maybe this problem hasn't been seen just because the pause function is rarely used.
So, the safe behavior would be to let the stream being SUSPENDED state at snd_pcm_stream_suspend() when it's in the PAUSED and has no INFO_RESUME capability. Then the application does re-prepare the stream like the running one.
But the question is what's expected at next. Should the application re-start? But it was paused. Should PCM core automatically move to pause? But most hardware can't move the pointer to any random position.
My gut feeling is just to treat like a normal error-restart, i.e. re-prepare / re-start. But I'm open and would like to hear more opinions.
Hi Takashi,
So in the current scenario what we see is that after resuming from S3, a pause-release action from the user results in a FE prepare() followed by the START trigger (and not a PAUSE-RELEASE trigger).
Libin's patch proposes to do a prepare() for the BE even in the case of a regular pause-release. But this might not be ideal since other drivers might have logic in the prepare() ioctl that might end up with errors.
Right.
So I am thinking maybe we can have some internal logic in the SOF prepare() callback that will also call the BE prepare() when the be->dpcm[stream].state is SND_SOC_DPCM_STATE_PAUSED? Would that make sense?
Yes, that would work, I guess. Eventually this might be needed to be addressed in ALSA core side, too, but it's good to have some fix beforehand in DPCM.
thanks,
Takashi