Messages in this thread | | | Subject | Re: [RFC PATCH] ALSA: compress: Fix gapless playback state machine | From | Jaroslav Kysela <> | Date | Thu, 11 Jun 2020 12:40:46 +0200 |
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Dne 11. 06. 20 v 11:44 Vinod Koul napsal(a): > On 11-06-20, 11:09, Jaroslav Kysela wrote: >> 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. > > Yeah sorry I overlooked that case and was thinking of it being invoked > from driver! > > Yes this would make the snd_compr_stop() behave incorrectly.. so this > cant be done as proposed. > > But we still need to set the draining stream state properly and I am > thinking below now: > > diff --git a/sound/core/compress_offload.c b/sound/core/compress_offload.c > index 509290f2efa8..9aba851732d7 100644 > --- a/sound/core/compress_offload.c > +++ b/sound/core/compress_offload.c > @@ -929,7 +929,9 @@ static int snd_compr_partial_drain(struct snd_compr_stream *stream) > } > > stream->next_track = false; > - return snd_compress_wait_for_drain(stream); > + retval = snd_compress_wait_for_drain(stream); > + stream->runtime->state = SNDRV_PCM_STATE_RUNNING; > + return retval; > }
I see a race possibility when the last track is too small and the driver signals the end-of-track twice. In this case the partial drain should not end with the running state. It would be probably better to separate partial / last track acknowledgements.
Jaroslav
-- Jaroslav Kysela <perex@perex.cz> Linux Sound Maintainer; ALSA Project; Red Hat, Inc.
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