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

[Takashi Iwai]

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;
		}
	}


Takashi