[PATCH] ASoC: fsl: sai: Reduce underrun when stream starts

[PATCH] ASoC: fsl: sai: Reduce underrun when stream starts

[Daniel Baluta]

From: Shengjiu Wang <shengjiu.wang@nxp.com>

Write initial words into SAI FIFO to reduce the underrun
error.

Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Signed-off-by: Daniel Baluta <daniel.baluta@nxp.com>
---
 sound/soc/fsl/fsl_sai.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/sound/soc/fsl/fsl_sai.c b/sound/soc/fsl/fsl_sai.c
index db9e0872f73d..99edbba4e8fa 100644
--- a/sound/soc/fsl/fsl_sai.c
+++ b/sound/soc/fsl/fsl_sai.c
@@ -503,7 +503,9 @@ static int fsl_sai_trigger(struct snd_pcm_substream *substream, int cmd,
 {
 	struct fsl_sai *sai = snd_soc_dai_get_drvdata(cpu_dai);
 	bool tx = substream->stream == SNDRV_PCM_STREAM_PLAYBACK;
+	unsigned int channels = substream->runtime->channels;
 	u32 xcsr, count = 100;
+	int i;
 
 	/*
 	 * Asynchronous mode: Clear SYNC for both Tx and Rx.
@@ -526,6 +528,11 @@ static int fsl_sai_trigger(struct snd_pcm_substream *substream, int cmd,
 		regmap_update_bits(sai->regmap, FSL_SAI_xCSR(tx),
 				   FSL_SAI_CSR_FRDE, FSL_SAI_CSR_FRDE);
 
+		for (i = 0; tx && i < channels; i++)
+			regmap_write(sai->regmap, FSL_SAI_TDR, 0x0);
+		if (tx)
+			udelay(10);
+
 		regmap_update_bits(sai->regmap, FSL_SAI_RCSR,
 				   FSL_SAI_CSR_TERE, FSL_SAI_CSR_TERE);
 		regmap_update_bits(sai->regmap, FSL_SAI_TCSR,
-- 
2.17.1

Re: [PATCH] ASoC: fsl: sai: Reduce underrun when stream starts

[Fabio Estevam]

Hi Daniel,

On Fri, Mar 8, 2019 at 1:09 PM Daniel Baluta <daniel.baluta@nxp.com> wrote:
>
> From: Shengjiu Wang <shengjiu.wang@nxp.com>
>
> Write initial words into SAI FIFO to reduce the underrun
> error.

Please provide a better explanation.

Why does performing these writes help?

Also, the commit message says "reduce", so it seems this is a
workaround instead of a proper fix?

Re: [PATCH] ASoC: fsl: sai: Reduce underrun when stream starts

[Daniel Baluta]

On Fri, Mar 8, 2019 at 6:16 PM Fabio Estevam <festevam@gmail.com> wrote:
>
> Hi Daniel,
>
> On Fri, Mar 8, 2019 at 1:09 PM Daniel Baluta <daniel.baluta@nxp.com> wrote:
> >
> > From: Shengjiu Wang <shengjiu.wang@nxp.com>
> >
> > Write initial words into SAI FIFO to reduce the underrun
> > error.
>
> Please provide a better explanation.

Hi Fabio,

Fair enough, will try to provide a better description in v2
that will also address your questions below.

>
> Why does performing these writes help?
>
> Also, the commit message says "reduce", so it seems this is a
> workaround instead of a proper fix?