Just to let you know my findings since two years . There is a closed source 
kernel  (in Linpus for Acer Aspire One) driver to handle this kind of small 
array microphone from Fortemedia (here on Acer Ferrari One 200).
There are in fact 4 channels ie 2 stereo signals (force channels_max to 4 in 
hda_intel and patch_realtek). This is done to let fmaudio kernel driver 
(heavily plugged into hda_intel, infringing on the gpl in various ways) do 
beam, noise processing and other nifty things.
I started works on this. Please tell me if you are interested in my hacks (I 
managed to get the 4 streams and record them then work in audacity to try to 
decipher the noise reduction). I also started work on a pulseaudio module (I do 
not think the audio postprocessing should be done in kernel) fmaaudiosma which 
I talked upon on pulseaudio ML but this was sent before I found about the 4 
channels trick.

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https://bugs.launchpad.net/bugs/1002978

Title:
  [meta-bug] Inverted Internal microphone (phase inversion)

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