Comment 3 for bug 1046412

Ubuntu for ac100 uses ucm config (placed in /usr/share/alsa/ucm/) for audio device (thanks to ogra!).
So I suppose we just need to add few lines to the config to enable internal mic (dmic):
                cset "name='DMIC En Capture Switch' on"
                cset "name='DMIC PreFilter Capture Switch' on"
                cset "name='DMICL Mix DMICL2ADC Capture Switch' on"
                cset "name='I2SOut Mux' 'ADC LR'"
                cset "name='DMIC Boost Volume' 100,100"
                cset "name='Rec Capture Volume' 100,100"
I'm not sure about Volume values (I don't have my ac100 with me and can't check what values are good - very high values can produse noise).

Useful links:
http://ac100.wikispaces.com/alsa_ucm
http://ac100.grandou.net/mixer_settings#recording_sound_from_integrated_dmic