Re: ASoC: amd: acp-pdm: full-scale burst on every DMIC capture start

[Robin Everaars]

> Could you please try attached patch?

Thanks. I checked the bound driver before building it and found an error in my
original report: I named acp-pdm.c, but that is not the path used by this
machine.

The PX13 is bound as follows:

  /sys/bus/platform/devices/acp_ps_pdm_dma.0/driver/module
    -> /sys/module/snd_ps_pdm_dma

  snd_ps_pdm_dma:
    sound/soc/amd/ps/snd-ps-pdm-dma.ko.xz
    platform alias acp_ps_pdm_dma

The attached patch changes sound/soc/amd/acp/acp-pdm.c, which builds
snd-acp-pdm. That module is installed but does not own this PCM, so applying the
patch as-is would not exercise the reported hardware.

The corresponding start sequence is acp63_start_pdm_dma() in
sound/soc/amd/ps/ps-pdm-dma.c. It also enables the PDM clock, decimator and DMA
without a settling interval. I can port the 300 ms delay and FIFO flush there
and test it, but I would prefer to test the exact shape you want upstream. Would
you send an equivalent patch for snd-ps-pdm-dma, 
or would you like me to prepare
the test diff?

One detail may also need handling in both versions. PAUSE_PUSH currently takes
the stop path and disables PDM. After moving PDM_ENABLE to prepare(),
PAUSE_RELEASE arms only the DMA, and ALSA does not necessarily call prepare()
between those commands. Should PAUSE_PUSH leave the decimator running, or
should PAUSE_RELEASE use a separate non-sleeping re-enable path?

Sorry for pointing the original report at the wrong driver. The measurements
and PCM are unchanged; only my source attribution was wrong.

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