linux-kernel - Re: [PATCH 16/29] staging: bcm2835-audio: Drop superfluous mutex lock during prepare

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Date:   Sat, 08 Sep 2018 18:12:58 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Stefan Wahren <stefan.wahren@...e.com>
Cc:     Eric Anholt <eric@...olt.net>,
        linux-rpi-kernel@...ts.infradead.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 16/29] staging: bcm2835-audio: Drop superfluous mutex lock during prepare

On Sat, 08 Sep 2018 15:40:41 +0200,
Stefan Wahren wrote:
> 
> Hi,
> 
> > Takashi Iwai <tiwai@...e.de> hat am 4. September 2018 um 17:58 geschrieben:
> > 
> > 
> > The chip->audio_mutex is used basically for protecting the opened
> > stream assignment, and the prepare callback is irrelevant with it.
> > 
> > Signed-off-by: Takashi Iwai <tiwai@...e.de>
> > ---
> >  drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c | 8 ++------
> >  1 file changed, 2 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c b/drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c
> > index 1f9c940f1cc3..9659c25b9f9d 100644
> > --- a/drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c
> > +++ b/drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c
> > @@ -218,8 +218,6 @@ static int snd_bcm2835_pcm_prepare(struct snd_pcm_substream *substream)
> >  	int channels;
> >  	int err;
> >  
> > -	mutex_lock(&chip->audio_mutex);
> > -
> >  	/* notify the vchiq that it should enter spdif passthrough mode by
> >  	 * setting channels=0 (see
> >  	 * https://github.com/raspberrypi/linux/issues/528)
> > @@ -233,7 +231,7 @@ static int snd_bcm2835_pcm_prepare(struct snd_pcm_substream *substream)
> >  				       runtime->rate,
> >  				       snd_pcm_format_width(runtime->format));
> >  	if (err < 0)
> > -		goto out;
> > +		return err;
> >  
> >  	memset(&alsa_stream->pcm_indirect, 0, sizeof(alsa_stream->pcm_indirect));
> >  
> > @@ -246,9 +244,7 @@ static int snd_bcm2835_pcm_prepare(struct snd_pcm_substream *substream)
> >  	alsa_stream->pos = 0;
> >  	alsa_stream->draining = false;
> >  
> > - out:
> > -	mutex_unlock(&chip->audio_mutex);
> > -	return err;
> > +	return 0;
> 
> looks like your are removing code which has been added in patch #14 ?

No, the patch #14 corrects the missing error path.  Without patch 14,
the error from prepare is ignored.  And this patch gets rid of the
superfluous mutex lock.


thanks,

Takashi