HelenOS sources
hda_get_amp_gain_mute 282 uspace/drv/audio/hdaudio/codec.c rc = hda_get_amp_gain_mute(codec, aw, 0x8000, &gmleft);
hda_get_amp_gain_mute 286 uspace/drv/audio/hdaudio/codec.c rc = hda_get_amp_gain_mute(codec, aw, 0xa000, &gmright);
hda_get_amp_gain_mute 318 uspace/drv/audio/hdaudio/codec.c rc = hda_get_amp_gain_mute(codec, aw, 0x0000 + i, &gmleft);
hda_get_amp_gain_mute 322 uspace/drv/audio/hdaudio/codec.c rc = hda_get_amp_gain_mute(codec, aw, 0x2000 + i, &gmright);
HelenOS homepage, sources at GitHub