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

[Nicolin Chen]

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?