I've got a similar problem, although I did get it to work on ONE boot... but after rebooting again it no longer detects..
my device is:
00:14.5 Multimedia audio controller: ATI Technologies Inc IXP SB400 AC'97 Audio Controller (rev 80)
and a lspci -ns:
00:14.5 0401: 1002:4370 (rev 80)
packages for alsa:
under Hardware - Sound, it was listed as ATI IXP AC97, now it says ATI IXP AC97 (not connected)
Not sure why it worked on one boot, but not now....
it's a laptop Acer Ferrari 4006
any help would be awesome!
ps. For those with same problem, when I updated my kernel is when it started to work.... but after a reboot it stopped.. so you may want to try a kernel update?