Comment 38 for bug 318942

Ok to follow up, I've got the built-in mic working. Starting from fresh 9.04 UNR image, I followed Maurico's instructions above to build/install alsa 1.0.19, with one change. In /etc/modprobe.d/alsa-base.conf instead of

options snd-hda-intel model=dell-m4-1

I put

options snd-hda-intel model=hp-m4

Found that here:
http://www.kernel.org/doc/Documentation/sound/alsa/HD-Audio-Models.txt
http://www.kernel.org/doc/Documentation/sound/alsa/ALSA-Configuration.txt

I also tried model=ref-no-jd and that worked too. This enabled a third option in the "Input Source" section of the mixer. In addition to "Mic" and "Front Mic" there's now "Line" which is the internal mic. Haven't tried the mic jack but everything else works.