[alsa-devel] softvol and snd_pcm_rewind() is broken

[Takashi Iwai]

At Fri, 18 Jul 2008 12:47:08 -0400,
Stewart Adam wrote:
> 
> I tried applying it but the two hunks failed - Is there a more recent
> patch available?

It is against the latest version of alsa-lib.


Takashi

> 
> Thanks,
> Stewart
> 
> 
> On Thu, 2008-07-17 at 11:56 +0200, Takashi Iwai wrote:
> > At Wed, 16 Jul 2008 16:30:04 +0200,
> > Lennart Poettering wrote:
> > > 
> > > Heya!
> > > 
> > > With 1.0.17rc3 snd_pcm_rewind() is broken for softvol as it seems:
> > > 
> > > - Sometimes the sound becomes heavily distorted after such a seek:
> > > 
> > >   http://mailman.alsa-project.org/pipermail/alsa-devel/2008-June/008860.html
> > > 
> > > - And snd_pcm_rewind() might return a value that is higher than was
> > >   passed in, which as far as I understood should never happen:
> > > 
> > >   http://mailman.alsa-project.org/pipermail/alsa-devel/2008-April/007308.html
> > > 
> > > These two issues might be caused by the same error.
> > > 
> > > Takashi, Jaroslav, how can I bribe you into fixing this? I'd love to
> > > release my new PulseAudio version soon which heavily relies on
> > > snd_pcm_rewind(), but unfortunately the most important driver (hda
> > > with softvol) makes the most problems with it. :-(
> > 
> > As mentioned earlier, the softvol itself is a simple plain plugin and
> > it has no code to do forward/rewind in itself.  Thus, if a bug is
> > present in softvol, it must be in the generic plugin code -- or there
> > can be a missing piece that the generic code doesn't cover.  I'm not
> > sure yet, as I didn't write that code.
> > 
> > The second problem, the bigger return size, looks like a thinko in the
> > code.  Try the patch below.
> > 
> > 
> > Takashi
> > 
> > ---
> > diff --git a/src/pcm/pcm_plugin.c b/src/pcm/pcm_plugin.c
> > index c73a02b..b5e940b 100644
> > --- a/src/pcm/pcm_plugin.c
> > +++ b/src/pcm/pcm_plugin.c
> > @@ -203,10 +203,10 @@ static snd_pcm_sframes_t snd_pcm_plugin_rewind(snd_pcm_t *pcm, snd_pcm_uframes_t
> >  	snd_pcm_sframes_t n = snd_pcm_mmap_hw_avail(pcm);
> >  	snd_pcm_sframes_t sframes;
> >  
> > -	if ((snd_pcm_uframes_t)n > frames)
> > -		frames = n;
> > -	if (frames == 0)
> > +	if (n <= 0 || frames == 0)
> >  		return 0;
> > +	if ((snd_pcm_uframes_t)n < frames)
> > +		frames = n;
> >  	
> >  	if (plugin->slave_frames)
> >  		sframes = plugin->slave_frames(pcm, (snd_pcm_sframes_t) frames);
> > @@ -236,10 +236,10 @@ static snd_pcm_sframes_t snd_pcm_plugin_forward(snd_pcm_t *pcm, snd_pcm_uframes_
> >  	snd_pcm_sframes_t n = snd_pcm_mmap_avail(pcm);
> >  	snd_pcm_uframes_t sframes;
> >  
> > -	if ((snd_pcm_uframes_t)n > frames)
> > -		frames = n;
> > -	if (frames == 0)
> > +	if (n <= 0 || frames == 0)
> >  		return 0;
> > +	if ((snd_pcm_uframes_t)n < frames)
> > +		frames = n;
> >  	
> >  	if (plugin->slave_frames)
> >  		sframes = plugin->slave_frames(pcm, (snd_pcm_sframes_t) frames);
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>