Update to 2.6.31-18.20 broke sound on MacBook Pro 5.4 in Ubuntu 9.10

[Mario Vukelic]

Not sure whether the culprit is the kernel package upgrade or the associated alsa backports upgrade, but sound stopped working after the reboot. alsamixer reports "no mixer elements found". Reverting to the previous kernel 2.6.31-17-generic and the associated alsa backports package fixes it (but one has to unmute the front speakers again in alsamixer, just like after initial installation).

I tried to use the hardware identifying command in https://wiki.ubuntu.com/DebuggingSoundProblems but it didn't work and I couldn't figure it out. The link to the alsa-info.sh script on the same page is dead. Here goes what I have, let me know if you need more.

lspci says:
00:08.0 Audio device: nVidia Corporation MCP79 High Definition Audio (rev b1)

/proc/asound/card0/codec#0 says:
Codec: Cirrus Logic CS4206
Vendor Id: 0x10134206
Subsystem Id: 0x106b4c00
Revision Id: 0x100301

ProblemType: Bug
Architecture: amd64
Date: Fri Jan 15 23:37:27 2010
DistroRelease: Ubuntu 9.10
InstallationMedia: Ubuntu 9.10 "Karmic Koala" - Release amd64 (20091027)
NonfreeKernelModules: nvidia wl
Package: linux-backports-modules-alsa-2.6.31-18-generic 2.6.31-18.20
ProcEnviron:
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 2.6.31-17.54-generic
SourcePackage: linux-backports-modules-2.6.31
Uname: Linux 2.6.31-17-generic x86_64

[Mario Vukelic (kreuzsakra)]

With 9.10 long EOL anyway, this problem went away in later Ubuntu versions