After updating the kernel on one of my computers today I discovered that
usb-audio via snd-pcm-oss over the snd-usb-audio ALSA drivers stopped
working (worked with 2.6.13, doesn't with 2.6.14-rc[12345]).
The weird part is that it only stopped working when using the driver
through the oss emulation and only for some programs. I've tried it with
all apps with native alsa support that I had installed, and all of them
worked. I also tried it with a few different apps with oss support, and
most of them worked (xine and mplayer) while one failed (mythmusic).
The symptoms is that no sound is heard while the app seems to believe
that everything is just fine. It also progresses through the song at
about 20x normal speed (i.e. it thinks its done playing a 4 minute song
after 12 seconds). The only difference I can come up with is that xine
and mplayer probably up-sample the audio to 48.000Hz while MythMusic
tries to play at 44.100Hz (the device is a TerraTec external USB <->
SPDIF interface).
I've used git's bisect command to try to find the exact problem, and it
seems to have been introduced by this commit:
7efd8bc800324a967a37e8a425433468b7f06adb
see also:
http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=7efd8bc800324a967a37e8a425433468b7f06adb
patch name: [ALSA] usb-audio: double-buffer all playback data
I'm not sure on how to fix it since the commit is quite big and cannot
be simply reversed with the current tree as there have been other
patches applied to the file afterwards. Comments/suggestions welcome...
Regards,
David H?rdeman
david (at) 2gen (dot) com
PS
Please CC me on any replies