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

David Henningsson launchpad.web at epost.diwic.se
Wed Jun 23 21:57:01 CEST 2010

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.

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.

// David
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