linux-kernel - digital microphone on google chromebook code name banon

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Message-ID: <CAHVeOW-TgaUctUE71jDSofBCM_O3dxrSvbCYLPRKm_eRpmY_MQ@mail.gmail.com>
Date:   Fri, 14 Feb 2020 14:26:57 -0500
From:   Chris Gorman <chrisjohgorman@...il.com>
To:     linux-kernel@...r.kernel.org
Subject: digital microphone on google chromebook code name banon

Hello All,

I have a problem with my laptop recording via the digital microphone.
I did try to explain the problem on
https://bugzilla.kernel.org/show_bug.cgi?id=95681, but I have heard no
response on the issue, so I am bugging the mailing list in hopes that
someone will have a magic fix for me. ;)

My laptop is a google chromebook, braswell, banon.  It is of the intel
strago family.  When I try to record all I get is white noise.  I can
reduce the level of noise via alsamixer, but I have to reduce all the
capture levels to 5 or lower.

I reached out to Sam McNally (thank you sam) from chromium regarding
his patch to cht_bsw_rt5645.c
adebb11139029ddf1fba6f796c4a476f17eacddc.  He was quite nice and
helpful.  According to Sam, the banon chromebooks dmic works with
their chromeos 4.9 and chromeos 5.4 kernels.  Unfortunately the dmic
still failed on my system when I tried the chromeos 5.4 kernel.
Perhaps the problem is my new coreboot 4.11 bios, whereas chrome uses
an older bios? I don't know.

Sam also pointed me to checking /sys/kernel/debug/clk/clk_summary.
While recording I get..

pmc_plt_clk_0                     0        0        0    19200000
       0     0  50000

and while playing everything's fine and I get...

pmc_plt_clk_0                     1        1        0    19200000
       0     0  50000

This is clearly the problem.  I don't know how to get the clock
working with the capture function though.

My kernel configs are ...

SOUND = y
SND = y
SND_SOC = y
SND_SOC_INTEL_MACH = y
SND_SST_ATOM_HIFI2_PLATFORM = y
SND_SST_ATOM_HIFI2_PLATFORM_ACPI = y
I2C = y
ACPI = y
X86_INTEL_LPSS = y
SND_SOC_ACPI = y
SND_SOC_INTEL_CHT_BSW_RT5645_MACH = y
SND_SOC_RT5645 = y
SND_SOC_DMIC = y

and I am running linux 5.5.0.  I welcome patches and suggestions, but
have not subscribed to the mailing list because of the volume of
emails, so please cc me with any response.

Thanks in advance.

Chris Gorman