Messages in this thread |  | | Date | Wed, 20 Nov 2019 15:33:50 +0100 | | From | Takashi Iwai <> | | Subject | Re: [PATCH v4 6/7] ALSA: aloop: Support selection of snd_timer instead of jiffies |
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On Wed, 20 Nov 2019 12:58:55 +0100, Andrew Gabbasov wrote: > +/* call in loopback->cable_lock */ > +static int loopback_snd_timer_open(struct loopback_pcm *dpcm) > +{ > + int err = 0; > + struct snd_timer_id tid = { > + .dev_class = SNDRV_TIMER_CLASS_PCM, > + .dev_sclass = SNDRV_TIMER_SCLASS_APPLICATION, > + }; > + struct snd_timer_instance *timeri; > + struct loopback_cable *cable = dpcm->cable; > + > + spin_lock_irq(&cable->lock); > + > + /* check if timer was already opened. It is only opened once > + * per playback and capture subdevice (aka cable). > + */ > + if (cable->snd_timer.instance) > + goto unlock; > + > + err = loopback_parse_timer_id(dpcm->loopback->timer_source, &tid); > + if (err < 0) { > + pcm_err(dpcm->substream->pcm, > + "Parsing timer source \'%s\' failed with %d", > + dpcm->loopback->timer_source, err); > + goto unlock; > + } > + > + cable->snd_timer.stream = dpcm->substream->stream; > + cable->snd_timer.id = tid; > + > + timeri = snd_timer_instance_new(dpcm->loopback->card->id); > + if (!timeri) { > + err = -ENOMEM; > + goto unlock; > + } > + /* The callback has to be called from another tasklet. If > + * SNDRV_TIMER_IFLG_FAST is specified it will be called from the > + * snd_pcm_period_elapsed() call of the selected sound card. > + * snd_pcm_period_elapsed() helds snd_pcm_stream_lock_irqsave(). > + * Due to our callback loopback_snd_timer_function() also calls > + * snd_pcm_period_elapsed() which calls snd_pcm_stream_lock_irqsave(). > + * This would end up in a dead lock. > + */ > + timeri->flags |= SNDRV_TIMER_IFLG_AUTO; > + timeri->callback = loopback_snd_timer_function; > + timeri->callback_data = (void *)cable; > + timeri->ccallback = loopback_snd_timer_event; > + > + /* snd_timer_close() and snd_timer_open() should not be called with > + * locked spinlock because both functions can block on a mutex. The > + * mutex loopback->cable_lock is kept locked. Therefore snd_timer_open() > + * cannot be called a second time by the other device of the same cable. > + * Therefore the following issue cannot happen: > + * [proc1] Call loopback_timer_open() -> > + * Unlock cable->lock for snd_timer_close/open() call > + * [proc2] Call loopback_timer_open() -> snd_timer_open(), > + * snd_timer_start() > + * [proc1] Call snd_timer_open() and overwrite running timer > + * instance > + */ > + spin_unlock_irq(&cable->lock); > + err = snd_timer_open(timeri, &cable->snd_timer.id, current->pid); > + if (err < 0) { > + pcm_err(dpcm->substream->pcm, > + "snd_timer_open (%d,%d,%d) failed with %d", > + cable->snd_timer.id.card, > + cable->snd_timer.id.device, > + cable->snd_timer.id.subdevice, > + err); > + snd_timer_instance_free(timeri); > + return err; > + } > + spin_lock_irq(&cable->lock); > + > + cable->snd_timer.instance = timeri; > + > + /* initialise a tasklet used for draining */ > + tasklet_init(&cable->snd_timer.event_tasklet, > + loopback_snd_timer_tasklet, (unsigned long)timeri);
This has to be set before snd_timer_open(). The callback might be called immediately after snd_timer_open().
thanks,
Takashi
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