linux-kernel - Re: [PATCH] ASoC: fsl_sai: Clean code for synchronize mode

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Message-ID: <20200804070345.GA27658@Asurada-Nvidia>
Date:   Tue, 4 Aug 2020 00:03:46 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Shengjiu Wang <shengjiu.wang@...il.com>
Cc:     Shengjiu Wang <shengjiu.wang@....com>,
        Linux-ALSA <alsa-devel@...a-project.org>,
        Timur Tabi <timur@...nel.org>, Xiubo Li <Xiubo.Lee@...il.com>,
        linuxppc-dev@...ts.ozlabs.org, Takashi Iwai <tiwai@...e.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Fabio Estevam <festevam@...il.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ASoC: fsl_sai: Clean code for synchronize mode

On Tue, Aug 04, 2020 at 12:22:53PM +0800, Shengjiu Wang wrote:

> > > Btw, do we need similar change for TRIGGER_STOP?
> >
> > This is a good question. It is better to do change for STOP,
> > but I am afraid that there is no much test to guarantee the result.

> Maybe we can do this change for STOP.

The idea looks good to me...(check inline comments)
 
> diff --git a/sound/soc/fsl/fsl_sai.c b/sound/soc/fsl/fsl_sai.c
> index 1c0e06bb3783..6e4be398eaee 100644
> --- a/sound/soc/fsl/fsl_sai.c
> +++ b/sound/soc/fsl/fsl_sai.c
> @@ -517,6 +517,37 @@ static int fsl_sai_hw_free(struct
> snd_pcm_substream *substream,
>         return 0;
>  }
> 
> +static void fsl_sai_config_disable(struct fsl_sai *sai, bool tx)
> +{
> +       unsigned int ofs = sai->soc_data->reg_offset;
> +       u32 xcsr, count = 100;
> +
> +       regmap_update_bits(sai->regmap, FSL_SAI_xCSR(tx, ofs),
> +                          FSL_SAI_CSR_TERE, 0);
> +
> +       /* TERE will remain set till the end of current frame */
> +       do {
> +               udelay(10);
> +               regmap_read(sai->regmap, FSL_SAI_xCSR(tx, ofs), &xcsr);
> +       } while (--count && xcsr & FSL_SAI_CSR_TERE);
> +
> +       regmap_update_bits(sai->regmap, FSL_SAI_xCSR(tx, ofs),
> +                          FSL_SAI_CSR_FR, FSL_SAI_CSR_FR);
> +
> +       /*
> +        * For sai master mode, after several open/close sai,
> +        * there will be no frame clock, and can't recover
> +        * anymore. Add software reset to fix this issue.
> +        * This is a hardware bug, and will be fix in the
> +        * next sai version.
> +        */
> +       if (!sai->is_slave_mode) {
> +               /* Software Reset for both Tx and Rx */

Remove "for both Tx and Rx"

>                 /* Check if the opposite FRDE is also disabled */
>                 regmap_read(sai->regmap, FSL_SAI_xCSR(!tx, ofs), &xcsr);
> +               if (sai->synchronous[tx] && !sai->synchronous[!tx] && !(xcsr & FSL_SAI_CSR_FRDE))
> +                       fsl_sai_config_disable(sai, !tx);

> +               if (sai->synchronous[tx] || !sai->synchronous[!tx] || !(xcsr & FSL_SAI_CSR_FRDE))
> +                       fsl_sai_config_disable(sai, tx);

The first "||" should probably be "&&".

The trigger() logic is way more complicated than a simple cleanup
in my opinion. Would suggest to split RMR part out of this change.

And for conditions like "sync[tx] && !sync[!tx]", it'd be better
to have a helper function to improve readability:

/**
 * fsl_sai_dir_is_synced - Check if stream is synced by the opposite stream
 *
 * SAI supports synchronous mode using bit/frame clocks of either Transmitter's
 * or Receiver's for both streams. This function is used to check if clocks of
 * current stream's are synced by the opposite stream.
 *
 * @sai: SAI context
 * @dir: direction of current stream
 */
static inline bool fsl_sai_dir_is_synced(struct fsl_sai *sai, int dir)
{
	int adir = (dir == TX) ? RX : TX;

	/* current dir in async mode while opposite dir in sync mode */
	return !sai->synchronous[dir] && sai->synchronous[adir];
}

Then add more comments in trigger:

static ...trigger()
{
	bool tx = substream->stream == SNDRV_PCM_STREAM_PLAYBACK;
	int adir = tx ? RX : TX;
	int dir = tx ? TX : RX;

	// ....
	{
		// ...

		/* Check if the opposite FRDE is also disabled */
		regmap_read(sai->regmap, FSL_SAI_xCSR(!tx, ofs), &xcsr);

		/*
		 * If opposite stream provides clocks for synchronous mode and
		 * it is inactive, disable it before disabling the current one
		 */
		if (fsl_sai_dir_is_synced(adir) && !(xcsr & FSL_SAI_CSR_FRDE))
			fsl_sai_config_disable(sai, adir);

		/*
		 * Disable current stream if either of:
		 * 1. current stream doesn't provide clocks for synchronous mode
		 * 2. current stream provides clocks for synchronous mode but no
		 *    more stream is active.
		 */
		if (!fsl_sai_dir_is_synced(dir) || !(xcsr & FSL_SAI_CSR_FRDE))
			fsl_sai_config_disable(sai, dir);

		// ...
	}
	// ....
}

Note, in fsl_sai_config_disable(sai, dir):
	bool tx = dir == TX;

Above all, I am just drafting, so please test it thoroughly :)