Re: [alsa-devel] [PATCH] ASoC: Intel: kbl_rt5663_rt5514_max98927: Add dmic format constraint

[Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>]

On 9/11/19 9:27 PM, Yu-Hsuan Hsu wrote:
> 24 bits recording from DMIC is not supported for KBL platform because
> the TDM slot between PCH and codec is 16 bits only. We should add a
> constraint to remove that unsupported format.

Humm, when you use DMICs they are directly connected to the PCH with a 
standard 1-bit PDM. There is no notion of TDM or slot.

It could very well be that the firmware/topology only support 16 bit (I 
vaguely recall another case where 24 bits was added), but the 
description in the commit message would need to be modified to make the 
reason for this change clearer.

> 
> Signed-off-by: Yu-Hsuan Hsu <yuhsuan@chromium.org>
> ---
>   sound/soc/intel/boards/kbl_rt5663_rt5514_max98927.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/sound/soc/intel/boards/kbl_rt5663_rt5514_max98927.c b/sound/soc/intel/boards/kbl_rt5663_rt5514_max98927.c
> index 74dda8784f1a01..67b276a65a8d2d 100644
> --- a/sound/soc/intel/boards/kbl_rt5663_rt5514_max98927.c
> +++ b/sound/soc/intel/boards/kbl_rt5663_rt5514_max98927.c
> @@ -400,6 +400,9 @@ static int kabylake_dmic_startup(struct snd_pcm_substream *substream)
>   	snd_pcm_hw_constraint_list(runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS,
>   			dmic_constraints);
>   
> +	runtime->hw.formats = SNDRV_PCM_FMTBIT_S16_LE;
> +	snd_pcm_hw_constraint_msbits(runtime, 0, 16, 16);
> +
>   	return snd_pcm_hw_constraint_list(substream->runtime, 0,
>   			SNDRV_PCM_HW_PARAM_RATE, &constraints_rates);
>   }
>