[alsa-devel] [PATCH] Two patches for Alsa-plugins (pulse)

[Takashi Iwai]

At Mon, 05 Jul 2010 08:06:45 +0200,
I wrote:
> 
> At Fri, 25 Jun 2010 12:41:46 +0200,
> David Henningsson wrote:
> > 
> > On 2010-06-24 08:42, Takashi Iwai wrote:
> > > At Wed, 23 Jun 2010 21:57:01 +0200,
> > > David Henningsson wrote:
> > >>
> > >> These two patches are being used in Ubuntu Lucid (released this April)
> > >> and are working well enough to have people asking us to backport them to
> > >> Karmic. Today I got an email, asking for the upstream status of one of
> > >> these patches, since he wanted them in Fedora. If posting them here
> > >> isn't the correct way to upstream them, please tell me so.
> > >>
> > >> The first one (Fix invalid buffer pointer return value) fixes broken logic:
> > >>
> > >> This patch improves recovering from underruns, and prevents hangs inside
> > >> snd_pcm_write* and snd_pcm_read* due to snd_pcm_avail* returning too
> > >> low values. It especially helps low latency situations.
> > > 
> > > This one looks OK.  Applied now.
> > 
> > Thanks!
> > 
> > >> The second one (Do not report underruns to the ALSA layer) is more a
> > >> change of behavior, which could be questioned. The arguments for
> > >> removing that code are these:
> > >>
> > >>  * If pulseaudio gets an underrun, the normal way to end that underrun
> > >> is to feed it with more buffers. This is different from the ALSA way of
> > >> dealing with underruns, which requires hardware buffer pointers to be reset.
> > >>  * In addition, underrun signals are delivered asynchronously from
> > >> pulseaudio. This means that there might be more buffers on the way to
> > >> pulseaudio when the underrun is reported, making the underrun obsolete.
> > >> Unfortunately, there is currently no known way to determine whether this
> > >> is the case or not.
> > > 
> > > I think this helps for normal use-cases, so it'd be good to apply.
> > > But, I prefer having a runtime option for such a behavior change
> > > (although the default value can be the new behavior).
> > > 
> > > Care to add it?
> > 
> > Sure, I can do that - it sounds like a good idea to have it configurable.
> > Just so I understand you right, exactly how do you expect the user /
> > application to configure it?
> 
> I suppose it can be simply added as an alsa-lib plugin config, i.e.
> in SND_PCM_PLUGIN_DEFINE_FUNC(pulse) of alsa-plugins/pulse/pcm_pulse.c,
> add the code like below:
> 
> 	int handle_underrun = 0;
> 	...
> 
> 	snd_config_for_each(i, next, conf) {
> 		...
> 		if (strcmp(id, "handle_underrun") == 0) {
> 			handle_underrun = snd_config_get_bool(n);
> 			if (handle_underrun < 0) {
> 				SNDERR("Invalid value for %s", id);
> 				return handle_underrun;
> 			}
> 			continue;
> 		}
> 	}

FYI, I modified the patch and applied to git tree right now.


thanks,

Takashi