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

[Yu-Hsuan Hsu]

Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx> æ
2019å9æ12æ éå äå9:02åéï
>
> 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.

(I sent it again because the previous email contains HTML subpart.
Sorry for the inconvenience.)

Thanks for the review! If I'm not mistaken, the microphone is attached
to external codec(rt5514) instead of PCH on Kabylake platform. So
there should be a TDM between DMICs and PCH. We can see in the
kabylake_ssp0_hw_params function, there are some operations about
setting tdm slot_width to 16 bits. Therefore, I think it only supports
S16_LE format for DMICs. Is it correct?
>
>
>
> >
> > Signed-off-by: Yu-Hsuan Hsu <yuhsuan@xxxxxxxxxxxx>
> > ---
> >   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);
> >   }
> >
>