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

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Date:   Wed, 10 Jun 2020 11:07:29 +0100
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     vkoul@...nel.org
Cc:     perex@...ex.cz, tiwai@...e.com, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org, broonie@...nel.org,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
Subject: [RFC PATCH] ALSA: compress: Fix gapless playback state machine

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

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);
 }
-- 
2.21.0