[alsa-devel] [PATCH] ASoC: fsl_sai: Fix noise when using EDMA

[Daniel Baluta]

On Fri, Sep 6, 2019 at 4:25 AM Nicolin Chen <nicoleotsuka at gmail.com> wrote:
>
> On Fri, Aug 30, 2019 at 11:09:00PM +0300, Daniel Baluta wrote:
> > From: Mihai Serban <mihai.serban at nxp.com>
> >
> > EDMA requires the period size to be multiple of maxburst. Otherwise the
> > remaining bytes are not transferred and thus noise is produced.
> >
> > We can handle this issue by adding a constraint on
> > SNDRV_PCM_HW_PARAM_PERIOD_SIZE to be multiple of tx/rx maxburst value.
> >
> > Cc: NXP Linux Team <linux-imx at nxp.com>
> > Signed-off-by: Mihai Serban <mihai.serban at nxp.com>
> > Signed-off-by: Daniel Baluta <daniel.baluta at nxp.com>
> > ---
> >  sound/soc/fsl/fsl_sai.c | 15 +++++++++++++++
> >  sound/soc/fsl/fsl_sai.h |  1 +
> >  2 files changed, 16 insertions(+)
> >
> > diff --git a/sound/soc/fsl/fsl_sai.c b/sound/soc/fsl/fsl_sai.c
> > index 728307acab90..fe126029f4e3 100644
> > --- a/sound/soc/fsl/fsl_sai.c
> > +++ b/sound/soc/fsl/fsl_sai.c
> > @@ -612,6 +612,16 @@ static int fsl_sai_startup(struct snd_pcm_substream *substream,
> >                          FSL_SAI_CR3_TRCE_MASK,
> >                          FSL_SAI_CR3_TRCE);
> >
> > +     /*
> > +      * some DMA controllers need period size to be a multiple of
> > +      * tx/rx maxburst
> > +      */
> > +     if (sai->soc_data->use_constraint_period_size)
> > +             snd_pcm_hw_constraint_step(substream->runtime, 0,
> > +                                        SNDRV_PCM_HW_PARAM_PERIOD_SIZE,
> > +                                        tx ? sai->dma_params_tx.maxburst :
> > +                                        sai->dma_params_rx.maxburst);
>
> I feel that PERIOD_SIZE could be used for some other cases than
> being related to maxburst....
>
> >  static const struct of_device_id fsl_sai_ids[] = {
> > diff --git a/sound/soc/fsl/fsl_sai.h b/sound/soc/fsl/fsl_sai.h
> > index b89b0ca26053..3a3f6f8e5595 100644
> > --- a/sound/soc/fsl/fsl_sai.h
> > +++ b/sound/soc/fsl/fsl_sai.h
> > @@ -157,6 +157,7 @@
> >
> >  struct fsl_sai_soc_data {
> >       bool use_imx_pcm;
> > +     bool use_constraint_period_size;
>
> ....so maybe the soc specific flag here could be something like
>         bool use_edma;
>
> What do you think?

I think your suggestion is a little bit better than what we have. But what if
in the future another DMA controler (not eDMA) will need the same constraint.

Wouldn't it be confusing?