HelenOS sources

hda_power_ctl_init  544 uspace/drv/audio/hdaudio/codec.c 		rc = hda_power_ctl_init(codec, fg);
hda_power_ctl_init  563 uspace/drv/audio/hdaudio/codec.c 				rc = hda_power_ctl_init(codec, aw);
HelenOS homepage, sources at GitHub