Public bug reported:

I have carefully read through these bugs:
  https://bugs.launchpad.net/ubuntu/+source/alsa-driver/+bug/337314
  https://bugs.launchpad.net/ubuntu/+source/pulseaudio/+bug/433633
  https://bugs.launchpad.net/alsa-driver/+bug/396563
They conflate a bunch of snd_hda_intel driver issues, and pulseaudio issues 
across many hardware platforms. However, some of these issues are quite 
separate between different chipsets. E.g. model=laptop does different things on 
different chipsets, and doesn't do a thing for my chipset ALC889A. See the full 
quirks list here:
  http://www.kernel.org/doc/Documentation/sound/alsa/HD-Audio-Models.txt

I am reporting this from a x86_64 install, but my sound was broken in
exactly the same way when I was running i386.

I have not found a published configuration, which makes the sound on my MacBook 
Pro 5,1 work completely. I have tried:
1) linux-backports-modules-alsa-generic   +   snd_hda_linux option "model=mb5"  
(same as autodetected),
2) default 2.6.31-15-generic   +   snd_hda_linux option "model=mb5".
In both:
 * (GOOD) Both left and right speakers work (and subwoofer too, I suspect).
 * (BAD) No jack sense: "cat /proc/asound/card*/codec*" is the same regardless 
of whether headphones are plugged in
 * (BAD) Speakers always on: Volume controls always enable + maximize 
Front+LFE+Surround outputs (in tandem), never touch headphones (which are muted 
by default, and labeled "HP" -- which I suspect breaks PulseAudio paths that 
depend on the string Headphones). The only manual way (i.e. using alsamixer) to 
silence the speakers is to 0 (but not mute) those three sliders in alsamixer, 
and then never to touch the PulseAudio volume controls ever again. That's sad.
 * (SLIGHTLY BAD) Headphones should be on by default, not to make users set 
them up.
 * (BAD) Headset microphones don't work. Apple extensively uses a 3.5 jack 
standard which combines stereo output and microphone input. This is supported 
by iPhones & co, and their computers. Apple, and many external vendors 
manufacture such headsets. The headset works automagically under MacOS, but 
fails to work under linux, no matter what input settings I choose.
3) linux-backports-modules-alsa-generic   +   snd_hda_linux option "model=mbp3" 
 (recommended by community page 
https://help.ubuntu.com/community/MacBook5-1/Karmic),
4) default 2.6.31-15-generic   +   snd_hda_linux option "model=mbp3".
In both:
 * (BAD) Only the right speaker works, and even that after switching alsamixer 
from 2 channels to 4 channels.
 * (BAD) No jack sense -- just as above
 * (OKAYISH) The system volume controls affect only the headphone volume. You 
are free to manually choose the speaker volume via "Surround". 
 * (SLIGHTLY BAD) If "4 channel" mode is what it takes to have some semblance 
of speaker sound, that should be on by default.
 * (BAD) Headset microphones don't work.
5) model=imac24 -- useless for this machine, the mixer settings are totally 
broken, still no jack sense.

In particular, the latest karmic backports have no effect on my
problems.

On the basis of the above, I'm changing the community docs to no longer
make a blanket recommendation for model=mbp3. People have to make a
choice between two different sets of issues.

In an ideal world:

1) The driver would support jack sense.
2) The driver would add an extra input for microphones connected through the 
output 3.5 jack. 
3) PulseAudio would automatically mute the speakers on headphones being plugged 
in.
4) PulseAudio would switch to the headset microphone when that's plugged in.
5) PulseAudio would provide overrides for both of those behaviors.

** Affects: alsa-driver (Ubuntu)
     Importance: Undecided
         Status: New

-- 
Poor support for MacBook Pro 5,1: no jack sense, no in-line headset 
microphones, broken volume control
https://bugs.launchpad.net/bugs/488103
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