linux-kernel - Re: [PATCH v2] ASoC: fsl_ssi: Fix bclk calculation for mono channel

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Message-ID: <20200615230912.GA16681@Asurada-Nvidia>
Date:   Mon, 15 Jun 2020 16:09:13 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Shengjiu Wang <shengjiu.wang@....com>
Cc:     timur@...nel.org, Xiubo.Lee@...il.com, festevam@...il.com,
        broonie@...nel.org, perex@...ex.cz, tiwai@...e.com,
        alsa-devel@...a-project.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] ASoC: fsl_ssi: Fix bclk calculation for mono channel

On Mon, Jun 15, 2020 at 01:56:18PM +0800, Shengjiu Wang wrote:
> For mono channel, SSI will switch to Normal mode.
> 
> In Normal mode and Network mode, the Word Length Control bits
> control the word length divider in clock generator, which is
> different with I2S Master mode (the word length is fixed to
> 32bit), it should be the value of params_width(hw_params).
> 
> The condition "slots == 2" is not good for I2S Master mode,
> because for Network mode and Normal mode, the slots can also
> be 2. Then we need to use (ssi->i2s_net & SSI_SCR_I2S_MODE_MASK)
> to check if it is I2S Master mode.

The fsl_ssi_set_bclk is only called when fsl_ssi_is_i2s_master,
though I agree that that line of comments sounds confusing now.

> So we refine the famula for mono channel, otherwise there

famula => formula?

> will be sound issue for S24_LE.
> 
> Fixes: b0a7043d5c2c ("ASoC: fsl_ssi: Caculate bit clock rate using slot number and width")
> Signed-off-by: Shengjiu Wang <shengjiu.wang@....com>
> ---
> changes in v2
> - refine patch for Network mode and Normal mode.
> 
>  sound/soc/fsl/fsl_ssi.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/sound/soc/fsl/fsl_ssi.c b/sound/soc/fsl/fsl_ssi.c
> index bad89b0d129e..cbf67d132fda 100644
> --- a/sound/soc/fsl/fsl_ssi.c
> +++ b/sound/soc/fsl/fsl_ssi.c
> @@ -678,7 +678,8 @@ static int fsl_ssi_set_bclk(struct snd_pcm_substream *substream,
>  	struct regmap *regs = ssi->regs;
>  	u32 pm = 999, div2, psr, stccr, mask, afreq, factor, i;
>  	unsigned long clkrate, baudrate, tmprate;
> -	unsigned int slots = params_channels(hw_params);
> +	unsigned int channels = params_channels(hw_params);
> +	unsigned int slots;
>  	unsigned int slot_width = 32;
>  	u64 sub, savesub = 100000;
>  	unsigned int freq;
> @@ -688,9 +689,15 @@ static int fsl_ssi_set_bclk(struct snd_pcm_substream *substream,
>  	/* Override slots and slot_width if being specifically set... */
>  	if (ssi->slots)
>  		slots = ssi->slots;
> -	/* ...but keep 32 bits if slots is 2 -- I2S Master mode */
> -	if (ssi->slot_width && slots != 2)
> -		slot_width = ssi->slot_width;
> +	else
> +		/* Apply two slots for mono channel, because DC = 2 */
> +		slots = (channels == 1) ? 2 : channels;
> +
> +	/* ...but keep 32 bits if I2S Master mode */
> +	if ((ssi->i2s_net & SSI_SCR_I2S_MODE_MASK) != SSI_SCR_I2S_MODE_MASTER ||
> +	    channels == 1)
> +		slot_width = ssi->slot_width ? ssi->slot_width :

This looks very complicated...can you review and try mine?
(Basically, take 32-bit out of default but force it later)

@@ -678,8 +678,9 @@ static int fsl_ssi_set_bclk(struct snd_pcm_substream *substream,
        struct regmap *regs = ssi->regs;
        u32 pm = 999, div2, psr, stccr, mask, afreq, factor, i;
        unsigned long clkrate, baudrate, tmprate;
-       unsigned int slots = params_channels(hw_params);
-       unsigned int slot_width = 32;
+       unsigned int channels = params_channels(hw_params);
+       unsigned int slot_width = params_width(hw_params);
+       unsigned int slots = 2;
        u64 sub, savesub = 100000;
        unsigned int freq;
        bool baudclk_is_used;
@@ -688,10 +689,16 @@ static int fsl_ssi_set_bclk(struct snd_pcm_substream *substream,
        /* Override slots and slot_width if being specifically set... */
        if (ssi->slots)
                slots = ssi->slots;
-       /* ...but keep 32 bits if slots is 2 -- I2S Master mode */
-       if (ssi->slot_width && slots != 2)
+       if (ssi->slot_width)
                slot_width = ssi->slot_width;
 
+       /*
+        * ...but force 32 bits for stereo audio. Note that mono audio is also
+        * sent in 2 slots via NORMAL mode, so check both slots and channels.
+        */
+       if (slots == 2 && channels == 2)
+               slot_width = 32;
+
        /* Generate bit clock based on the slot number and slot width */
        freq = slots * slot_width * params_rate(hw_params);