Rockchip/rk3399-gru-sound: Use 48KHz sample rate for all devices

[alpernebbi]

The rk3399-gru-kevin board has problems when trying to simultaneously playback and record audio with the default PulseAudio sample rate of 44.1KHz. When the following command is run, the playback starts a few seconds after the recording finishes.

arecord -vvv -d 4 /dev/null & sleep 0.2; speaker-test -l 1 -p 100000 -t sine

When the sample rates are set to 48KHz either with PA configuration or in the UCM, playback and recording both start immediately. Another example is when a music player is running and we start arecord, the music starts stuttering but arecord can't record anything either.

Apparently, this is a hardware limitation due to the I2S lines being shared between the devices. Set all the device rates to 48KHz like Chrome OS does to make things work smoothly.

[1] https://chromium-review.googlesource.com/389695
[2] https://chromium-review.googlesource.com/898682

[perexg]

It should be handled in the driver - if the rate is already set in one direction, the driver should lock this rate for the other direction, too. I would fix the driver at first.

[alpernebbi]

if the rate is already set in one direction, the driver should lock this rate for the other direction

That sounds reasonable, I'll try to do it. But setting all rates to 44100 in the UCM config still results in the problematic behaviour, does that mean anything to you?

[perexg]

If you can reproduce the problem using different applications and ALSA utilities, it looks like a driver issue.