Cherry Trail + RT5645 devices analog microphone not working.

[Hans de Goede <hdegoede@redhat.com>]

Hi Bard,

I've been looking into getting the microphone to work on
some Cherry Trail + RT5645 devices with what appears to
be a simple analog microphone.

You can see the microphone on one of the models I'm trying
to get it to work on soldered onto the right side of the PCB
here: https://i.imgur.com/bJzBQWe.jpg

I'm using this ucm config:

https://fedorapeople.org/~jwrdegoede/chtrt5645/

Which is basically Pierre-Louis Bossart's config from:
https://github.com/plbossart/UCM

Adjusted because the devices all have a mono speaker.

I've been trying to get this to work myself and I can get
some sound while recording by adding:

                 cset "name='RECMIXL BST2 Switch' on"
                 cset "name='RECMIXR BST2 Switch' on"

But then I mainly get noise, I do get some sound from the
microphone if I talk really really loudly, but it is
barely above the noise-floor. I've the feeling that BST2
is only picking up the microphone via cross-talk and
that BST1 indeed is the correct input, but for some reason
I get complete silence when recording when only BST1 is
selected in the RECMIXR, and yes I've checked / set the
"IN1 boost volume".

TL;DR: I'm trying to get an analog mic to work on 3
different models Cherry Trail + RT5645 devices and I've
been unable to get this to work. I've put a registerdump
of the rt5645 with gnome-sound-recorder running here:
https://fedorapeople.org/~jwrdegoede/rt5645-mic-red.dump

Any insights / help with this would be very much
welcome.

Regards,

Hans