On Thu, 05 Sep 2024 13:01:11 +0200,
Chancel Liu wrote:
>
> > > > > Hi Takashi,
> > > > >
> > > > > Thanks for your reply and suggestions. Finally we have found the root
> > cause.
> > > > > Seems it's related to both drivers and alsa-lib.
> > > > >
> > > > > When two dmix clients run in parallel we get two direct dmix instances.
> > > > > 1st dmix instance:
> > > > > snd_pcm_dmix_open()
> > > > > snd_pcm_direct_initialize_slave()
> > > > > save_slave_setting()
> > > > > Since the driver we are using has SND_PCM_INFO_RESUME flag,
> > > > > dmix->spcm->info has this flag. Then this flag is cleared in
> > > > dmix->shmptr->s.info.
> > > > >
> > > > > 2nd dmix instance:
> > > > > snd_pcm_dmix_open()
> > > > > snd_pcm_direct_open_secondary_client()
> > > > > copy_slave_setting()
> > > > > 2nd dmix->spcm->info is copied from dmix->shmptr->s.info so it doesn'
> > > > > has this flag.
> > > > >
> > > > > If 1st dmix instance resumes firstly it should implement recovery of
> > > > > slave pcm in snd_pcm_direct_slave_recover(). Because 1st
> > > > > dmix->spcm->info has
> > > > > SND_PCM_INFO_RESUME，snd_pcm_resume(direct->spcm) can be called
> > > > > correctly to resume slave pcm.
> > > >
> > > > ... and immediately stop the stream, then prepare and restart as a usual
> > > > restart.
> > > >
> > > > > However if 2nd dmix instance resumes firstly,
> > > > > snd_pcm_resume(direct->spcm) will not be called because it's
> > > > > spcm->info doesn't has SND_PCM_INFO_RESUME flag. The 1st dmix
> > instance
> > > > > assumes someone else already did recovery so
> > > > > snd_pcm_resume(direct->spcm) won't be called neither. In result the
> > > > > slave pcm fails to resume.
> > > >
> > > > Something wrong happening here, then.
> > > >
> > > > In dmix, there is no hardware resume at all, but it's always a restart of the
> > > > stream. The call of snd_pcm_resume() is only temporarily for
> > inconsistencies
> > > > that can be a problem on some drivers (IIRC dmaengine stuff). That said,
> > > > dmix does a kind of fake resume, stops and restarts the stream cleanly on
> > the
> > > > first instance. On the second instance, it's already recovered, hence it
> > bails
> > > > out.
> > > >
> > > > If poll() hangs on the second instance, there can be some other problem.
> > > > Maybe the resume -> stop -> restart sequence doesn't work with your
> > driver
> > > > well?
> > > >
> > >
> > > Our dma driver will do PAUSE in system suspend and requires doing RESUME
> > in
> > > system resume. Current problem is that snd_pcm_resume() is not called by
> > both
> > > 1st instance and 2nd instance.
> >
> > That's weird. Are you really testing with the latest alsa-lib code?
> >
> > If application doesn't call snd_pcm_resume(), it means that the PCM
> > state isn't set to SUSPENDED, so it pretends as if still running.
> >
> > Or if you mean that snd_pcm_resume() to the slave PCM isn't called
> > (even though snd_pcm_resume() is called for the dmix PCM), check
> > whether snd_pcm_direct_slave_recover() gets called, especially at the
> > point:
> >
> > /* some buggy drivers require the device resumed before prepared;
> > * when a device has RESUME flag and is in SUSPENDED state,
> > resume
> > * here but immediately drop to bring it to a sane active state.
> > */
> > if (state == SND_PCM_STATE_SUSPENDED &&
> > (direct->spcm->info & SND_PCM_INFO_RESUME)) {
> > snd_pcm_resume(direct->spcm);
> > snd_pcm_drop(direct->spcm);
> > snd_pcm_direct_timer_stop(direct);
> > snd_pcm_direct_clear_timer_queue(direct);
> > }
> >
> > Try to put debug prints or catch via breakpoint whether this code path
> > is executed.
> >
> > Also, does the issue happen with the latest 6.11-rc kernel, too?
> > If yes, what if you drop SNDRV_PCM_INFO_RESUME bit flag in the driver
> > side? Does the problem persist, or it works?
> >
>
> I'm working on kernel 6.6 and alsa-lib v1.2.11. It's not so outdated I think and
> then I will try to switch on the latest version.
>
> Indeed I did some debug on this part. Please see my comments inline.
>
> int snd_pcm_direct_slave_recover(snd_pcm_direct_t *direct)
> {
> ...
>
> /* [Chancel]
> * When two dmix clients run in parallel we get two direct dmix instances.
> * 1st dmix->spcm->info has SND_PCM_INFO_RESUME flag but 2nd dmix doesn't.
OK, that must be the cause. It's because the second open copies the
saved shmem->s.info into spcm->info at its open time while we already
dropped the INFO_RESUME bit. All the rest behavior are side effect of
this inconsistency.
I guess dropping the INFO_RESUME bit at hw_params and hw_refine should
work instead. A totally untested fix is below.
(And I believe the drop of INFO_PAUSE should be handled similarly,
too, instead of dropping spcm->info bit there.)
Takashi
--- a/src/pcm/pcm_direct.c
+++ b/src/pcm/pcm_direct.c
@@ -1018,6 +1018,7 @@ int snd_pcm_direct_hw_refine(snd_pcm_t *pcm, snd_pcm_hw_params_t *params)
}
dshare->timer_ticks = hw_param_interval(params, SND_PCM_HW_PARAM_PERIOD_SIZE)->max / dshare->slave_period_size;
params->info = dshare->shmptr->s.info;
+ params->info &= ~SND_PCM_INFO_RESUME;
#ifdef REFINE_DEBUG
snd_output_puts(log, "DMIX REFINE (end):\n");
snd_pcm_hw_params_dump(params, log);
@@ -1031,6 +1032,7 @@ int snd_pcm_direct_hw_params(snd_pcm_t *pcm, snd_pcm_hw_params_t * params)
snd_pcm_direct_t *dmix = pcm->private_data;
params->info = dmix->shmptr->s.info;
+ params->info &= ~SND_PCM_INFO_RESUME;
params->rate_num = dmix->shmptr->s.rate;
params->rate_den = 1;
params->fifo_size = 0;
@@ -1183,8 +1185,6 @@ static void save_slave_setting(snd_pcm_direct_t *dmix, snd_pcm_t *spcm)
COPY_SLAVE(buffer_time);
COPY_SLAVE(sample_bits);
COPY_SLAVE(frame_bits);
-
- dmix->shmptr->s.info &= ~SND_PCM_INFO_RESUME;
}
#undef COPY_SLAVE
