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

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Date:   Wed, 10 Jun 2020 12:40:08 +0200
From:   Jaroslav Kysela <perex@...ex.cz>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        vkoul@...nel.org
Cc:     tiwai@...e.com, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org, broonie@...nel.org
Subject: Re: [RFC PATCH] ALSA: compress: Fix gapless playback state machine

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 =  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
> 6  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?

					Jaroslav



> 
> Fixes: f44f2a5417b2 ("ALSA: compress: fix drain calls blocking other compress functions (v6)")
> Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
> ---
> 
> I wonder who did gapless work on upstream so far?
> 
>   include/sound/compress_driver.h | 2 +-
>   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)
>   	if (snd_BUG_ON(!stream))
>   		return;
>   
> -	stream->runtime->state = SNDRV_PCM_STATE_SETUP;
> +	stream->runtime->state = SNDRV_PCM_STATE_RUNNING;
>   
>   	wake_up(&stream->runtime->sleep);
>   }
> 


-- 
Jaroslav Kysela <perex@...ex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.