Comment 9 for bug 1329014

http://www.alsa-project.org/alsa-doc/alsa-lib/pcm_plugins.html

since pulseaudio open front, iec958 for both playback and capture at the same time

you need to ensure those front and iec958 can be open at the same time by using asymmetric plugin so the those controls in hook plugin are used for playback only

http://git.alsa-project.org/?p=alsa-lib.git;a=commitdiff;h=ea020c3b2e678f2a29df468ec7da09f9d5785194;hp=922ff0da833e726054df2fc87abdc201fbc5e21b