ibook sound, limping mixer

in case this is of any use to anyone:

i've attached /dev/mixer code to talk to the dac3550a chip through some
i2c interface.  it just calls i2c bus write operations.

the lmsensors package provides an apple 'keywest' i2c controller
interface, which is a polling driver which appears to do the
same stuff as the PPCI2CInterface.cpp from IO/Drivers/.. in darwin

it all seems simple enough.  i hacked up a simple i2c driver merged into
the mixer code from above, cut apart dmasound to eliminate the mixer
device and extraneous stuff, and added the appropriate missing
KL1_AUDIO_XXX and KL1_I2S_) bits to arch/ppc/kernel/feature.c (in
feature_bits_keylargo[], under FEATURE_Sound_xxx  so the daca gets powered
up)

then i rebooted and had sound and a mixer device, and was able to
hear some sound, fiddle with the mixer controls, and then hear no sound
once or twice i was able to reenable sound by randomly fiddling with the
mixer.

so apparently SOME data was getting across the i2c bus to the daca chip,
but probably it was reading trash.

since the dac3550a has write-only i2c registers, its pretty hard to debug
the i2c interface.  probably if someone puts an oscilloscope probe on the
i2c bus signals it should all become clear.

--conrad