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

[Jaroslav Kysela]

Dne 11. 06. 20 v 10:46 Charles Keepax napsal(a):
> On Wed, Jun 10, 2020 at 04:28:20PM +0530, Vinod Koul wrote:
>> On 10-06-20, 12:40, 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?
>>
>> It is supposed to be invoked by driver when partial drain is complete..
>> both intel and sprd driver are calling this. snd_compr_stop is stop
>> while draining case so legit
>>
> 
> Not sure I follow this statement, could you elaborate a bit?
> snd_compr_stop putting the state to RUNNING seems fundamentally
> broken to me, the whole point of snd_compr_stop is to take the
> state out of RUNNING.

Yes. I agree. It seems that the acknowledge for the partial drain should be 
handled differently.

				Jaroslav

> 
> Thanks,
> Charles
> 


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