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

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Date:   Wed, 10 Jun 2020 11:56:58 +0100
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Jaroslav Kysela <perex@...ex.cz>, 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



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 =  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?

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

> 
>                      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);
>>   }
>>
> 
>