From the ALSA wiki
Powermac, PowerBook G3/G4 and iMac/iBook
Use the very latest CVS, this driver is under development. You need the module snd-powermac.
There is experimental support for auto-muting the speakers when headphones are plugged in on the PowerBooks - it can be disabled by a mixer switch.
On the Pismo G3, I found I had to toggle "MIC-BOOST" in alsamixer once to get sound out of it - this small buglet is probably going to be squshed soon.
- Jörn Nettingsmeier <firstname.lastname@example.org>