From: Takashi Iwai <tiwai@suse.de>
To: Andrew Gabbasov <andrew_gabbasov@mentor.com>
Cc: <alsa-devel@alsa-project.org>, <linux-kernel@vger.kernel.org>,
"Jaroslav Kysela" <perex@perex.cz>, Takashi Iwai <tiwai@suse.com>,
Timo Wischer <twischer@de.adit-jv.com>
Subject: Re: [PATCH v4 6/7] ALSA: aloop: Support selection of snd_timer instead of jiffies
Date: Wed, 20 Nov 2019 15:33:50 +0100 [thread overview]
Message-ID: <s5hh82y8vn5.wl-tiwai@suse.de> (raw)
In-Reply-To: <20191120115856.4125-7-andrew_gabbasov@mentor.com>
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
next prev parent reply other threads:[~2019-11-20 14:33 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-20 11:58 [PATCH v4 0/7] ALSA: aloop: Support sound timer as clock source instead of jiffies Andrew Gabbasov
2019-11-20 11:58 ` [PATCH v4 1/7] ALSA: aloop: Describe units of variables Andrew Gabbasov
2019-11-20 11:58 ` [PATCH v4 2/7] ALSA: aloop: Support return of error code for timer start and stop Andrew Gabbasov
2019-11-20 11:58 ` [PATCH v4 3/7] ALSA: aloop: Use callback functions for timer specific implementations Andrew Gabbasov
2019-11-20 11:58 ` [PATCH v4 4/7] ALSA: aloop: Rename all jiffies timer specific functions Andrew Gabbasov
2019-11-20 11:58 ` [PATCH v4 5/7] ALSA: aloop: Move CABLE_VALID_BOTH to the top of file Andrew Gabbasov
2019-11-20 11:58 ` [PATCH v4 6/7] ALSA: aloop: Support selection of snd_timer instead of jiffies Andrew Gabbasov
2019-11-20 11:58 ` [PATCH v4 7/7] ALSA: aloop: Support runtime change of snd_timer via info interface Andrew Gabbasov
2019-11-20 14:33 ` Takashi Iwai [this message]
2019-11-20 15:21 ` [PATCH v4 6/7] ALSA: aloop: Support selection of snd_timer instead of jiffies Andrew Gabbasov
2019-11-20 15:32 ` Takashi Iwai
2019-11-20 15:39 ` Andrew Gabbasov
2019-11-20 15:58 ` Takashi Iwai
2019-11-20 17:56 ` Andrew Gabbasov
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