Comment 4 for bug 1420988

Here is a solution that seems to work for me (Acer Travelmate B115):
add the line [code]options snd-hda-intel model=dell-headset-multi[/code]
in the file called /etc/modprobe.d/alsa-base.conf (or create the file if it doen't exist
In my case that makes internal microphone and headset microphone available. Automatic switching between the two is not perfect but in case it doesn't switch automatically I can fix it in pavucontrol.
Hope it helps in your environment, too!