Hello Takashi, > -----Original Message----- > From: Takashi Iwai [mailto:tiwai@xxxxxxx] > Sent: Wednesday, November 20, 2019 5:34 PM > To: Gabbasov, Andrew > Cc: alsa-devel@xxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Jaroslav > Kysela; Takashi Iwai; Timo Wischer > Subject: Re: [PATCH v4 6/7] ALSA: aloop: Support selection of snd_timer > instead of jiffies > > 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(). This tasklet is used/scheduled only in ccallback (not regular tick callback), and only for SNDRV_TIMER_EVENT_MSTOP event. Can this event really happen immediately after snd_timer_open()? Thanks! Best regards, Andrew _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx https://mailman.alsa-project.org/mailman/listinfo/alsa-devel
