Re: [RFC PATCH] ALSA: compress: Fix gapless playback state machine

[Srinivas Kandagatla]

On 10/06/2020 11:40, Jaroslav Kysela wrote:
> Dne 10. 06. 20 v 12:07 Srinivas Kandagatla napsal(a):
> > For gapless playback call to snd_compr_drain_notify() after
> > partial drain should put the state to SNDRV_PCM_STATE_RUNNING
> > rather than SNDRV_PCM_STATE_SETUP as the driver is ready to
> > process the buffers for new track.
> >
> > With existing code, if we are playing 3 tracks in gapless, after
> > partial drain finished on previous track 1 the state is set to
> > SNDRV_PCM_STATE_SETUP which is then moved to SNDRV_PCM_STATE_PREPARED
> > after data write. With this state calls to snd_compr_next_track() and
> > few other calls will fail as they expect the state to be in
> > SNDRV_PCM_STATE_RUNNING.
> >
> > Here is the sequence of events and state transitions:
> >
> > 1. set_params (Track 1), state =Â SNDRV_PCM_STATE_SETUP
> > 2. set_metadata (Track 1), no state change, state = SNDRV_PCM_STATE_SETUP
> > 3. fill and trigger start (Track 1), state = SNDRV_PCM_STATE_RUNNING
> > 4. set_next_track (Track 2), state = SNDRV_PCM_STATE_RUNNING
> > 5. partial_drain (Track 1), state = SNDRV_PCM_STATE_SETUP
> > 6Â snd_compr_drain_notify (Track 1), state = SNDRV_PCM_STATE_SETUP
> > 7. fill data (Track 2), state = SNDRV_PCM_STATE_PREPARED
> > 8. set_metadata (Track 3), no state change, state = 
> > SNDRV_PCM_STATE_PREPARED
> > 9. set_next_track (Track 3), !! FAILURE as state != 
> > SNDRV_PCM_STATE_RUNNING
>
>
> The snd_compr_drain_notify() is called only from snd_compr_stop(). 
> Something is missing in this sequence?

snd_compr_drain_notify() can also be called by drivers to notify when 
partial drain is finished. In this case its called from qcom compress 
driver.

--srini

>  ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ Jaroslav
>
>
>
> > Fixes: f44f2a5417b2 ("ALSA: compress: fix drain calls blocking other 
> > compress functions (v6)")
> > Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
> > ---
> >
> > I wonder who did gapless work on upstream so far?
> >
> > Â include/sound/compress_driver.h | 2 +-
> > Â 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/include/sound/compress_driver.h 
> > b/include/sound/compress_driver.h
> > index 6ce8effa0b12..eabac33864c2 100644
> > --- a/include/sound/compress_driver.h
> > +++ b/include/sound/compress_driver.h
> > @@ -182,7 +182,7 @@ static inline void snd_compr_drain_notify(struct 
> > snd_compr_stream *stream)
> > ÂÂÂÂÂ if (snd_BUG_ON(!stream))
> > ÂÂÂÂÂÂÂÂÂ return;
> > -ÂÂÂ stream->runtime->state = SNDRV_PCM_STATE_SETUP;
> > +ÂÂÂ stream->runtime->state = SNDRV_PCM_STATE_RUNNING;
> > ÂÂÂÂÂ wake_up(&stream->runtime->sleep);
> > Â }