2019-03-08 16:10:35

by Daniel Baluta

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

From: Shengjiu Wang <[email protected]>

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

Signed-off-by: Shengjiu Wang <[email protected]>
Signed-off-by: Daniel Baluta <[email protected]>
---
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

2019-03-08 16:16:43

by Fabio Estevam

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

Hi Daniel,

On Fri, Mar 8, 2019 at 1:09 PM Daniel Baluta <[email protected]> wrote:
>
> From: Shengjiu Wang <[email protected]>
>
> 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?

2019-03-08 16:27:56

by Daniel Baluta

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

On Fri, Mar 8, 2019 at 6:16 PM Fabio Estevam <[email protected]> wrote:
>
> Hi Daniel,
>
> On Fri, Mar 8, 2019 at 1:09 PM Daniel Baluta <[email protected]> wrote:
> >
> > From: Shengjiu Wang <[email protected]>
> >
> > 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?