RE: [alsa-devel] [PATCH] ASoC: bdw-rt5677: channel constraint support

[Lu, Brent]

> >
> > It's not only the mismatch but also the design limitation. According
> > to the information from google, the board (samus) only uses two
> > microphone so
> > 3 or 4 channel recording are not supported. That's the reason we
> > leverage the constraint from other machine driver (like
> > kbl_da7219_max98357a.c) to remove the 3 and 4 channel recording option.
> 
> The design limitation is already handled by the fact that the SSP operates in
> 2ch mode, so it's a different case from KBL where indeed the DMIC-based
> back-end can support 4 channels.
> 
> >
> > The difference after the constraint is implemented is that the
> > snd_pcm_hw_params_set_channels() function will return error (Invalid
> > argument) when channel number is 3 or 4 so the application knows the
> > configuration is not supported.
> 
> I get the error, I am just wondering if the fix is at the right location. I'll look
> into it, give me until tomorrow.

I think I got your point. I cherry-pick these commits back to v3.14 branch to fix
the FE/BE mismatch without adding constraint in machine driver. Thanks.

b073ed4e ASoC: soc-pcm: DPCM cares BE format
f4c277b8 ASoC: soc-pcm: DPCM cares BE channel constraint
4f2bd18b ASoC: dpcm: extend channel merging to the backend cpu dai
435ffb76 ASoC: dpcm: rework runtime stream merge
baacd8d1 ASoC: dpcm: add rate merge to the BE stream merge