linux-kernel - Re: [PATCH] ASoC: fsl_sai: Fix noise when using EDMA

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Date:   Thu, 5 Sep 2019 18:24:39 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Daniel Baluta <daniel.baluta@....com>
Cc:     broonie@...nel.org, festevam@...il.com, Xiubo.Lee@...il.com,
        shengjiu.wang@....com, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org, timur@...nel.org,
        mihai.serban@...il.com, Mihai Serban <mihai.serban@....com>,
        NXP Linux Team <linux-imx@....com>
Subject: Re: [PATCH] ASoC: fsl_sai: Fix noise when using EDMA

On Fri, Aug 30, 2019 at 11:09:00PM +0300, Daniel Baluta wrote:
> From: Mihai Serban <mihai.serban@....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@....com>
> Signed-off-by: Mihai Serban <mihai.serban@....com>
> Signed-off-by: Daniel Baluta <daniel.baluta@....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?