linux-kernel - Re: [PATCH v2 3/8] ASoC: cs42l42: Ensure MCLKint is a multiple of the sample rate

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Message-ID: <6fa372b6-f8e7-aaf8-dee4-bc0dde2cb931@linux.intel.com>
Date:   Wed, 18 Jan 2023 10:46:59 -0600
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Stefan Binding <sbinding@...nsource.cirrus.com>,
        Mark Brown <broonie@...nel.org>
Cc:     alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        patches@...nsource.cirrus.com,
        Richard Fitzgerald <rf@...nsource.cirrus.com>
Subject: Re: [PATCH v2 3/8] ASoC: cs42l42: Ensure MCLKint is a multiple of the
 sample rate



On 1/18/23 10:04, Stefan Binding wrote:
> From: Richard Fitzgerald <rf@...nsource.cirrus.com>
> 
> The chosen clocking configuration must give an internal MCLK (MCLKint)
> that is an integer multiple of the sample rate.
> 
> On I2S each of the supported bit clock frequencies can only be generated
> from one sample rate group (either the 44100 or the 48000) so the code
> could use only the bitclock to look up a PLL config.
> 
> The relationship between sample rate and bitclock frequency is more
> complex on Soundwire and so it is possible to set a frame shape to
> generate a bitclock from the "wrong" group. For example 2*147 with a
> 48000 sample rate would give a bitclock of 14112000 which on I2S
> could only be derived from a 44100 sample rate.

The explanation is a bit convoluted, clearly the 147-row configuration
was only meant to be used with 44100 kHz. I don't think 48kHz can be
supported without using the source- or sink-controlled async modes.

This is still a valid change so:

Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>

> Signed-off-by: Richard Fitzgerald <rf@...nsource.cirrus.com>
> Signed-off-by: Stefan Binding <sbinding@...nsource.cirrus.com>



> ---
>  sound/soc/codecs/cs42l42.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/sound/soc/codecs/cs42l42.c b/sound/soc/codecs/cs42l42.c
> index 82aa11d6937be..939f8bcc222c0 100644
> --- a/sound/soc/codecs/cs42l42.c
> +++ b/sound/soc/codecs/cs42l42.c
> @@ -653,7 +653,8 @@ static const struct cs42l42_pll_params pll_ratio_table[] = {
>  	{ 24576000, 1, 0x03, 0x40, 0x000000, 0x03, 0x10, 12288000, 128, 1}
>  };
>  
> -static int cs42l42_pll_config(struct snd_soc_component *component, unsigned int clk)
> +static int cs42l42_pll_config(struct snd_soc_component *component, unsigned int clk,
> +			      unsigned int sample_rate)
>  {
>  	struct cs42l42_private *cs42l42 = snd_soc_component_get_drvdata(component);
>  	int i;
> @@ -668,6 +669,10 @@ static int cs42l42_pll_config(struct snd_soc_component *component, unsigned int
>  	}
>  
>  	for (i = 0; i < ARRAY_SIZE(pll_ratio_table); i++) {
> +		/* MCLKint must be a multiple of the sample rate */
> +		if (pll_ratio_table[i].mclk_int % sample_rate)
> +			continue;
> +
>  		if (pll_ratio_table[i].sclk == clk) {
>  			cs42l42->pll_config = i;
>  
> @@ -893,6 +898,7 @@ static int cs42l42_pcm_hw_params(struct snd_pcm_substream *substream,
>  	struct cs42l42_private *cs42l42 = snd_soc_component_get_drvdata(component);
>  	unsigned int channels = params_channels(params);
>  	unsigned int width = (params_width(params) / 8) - 1;
> +	unsigned int sample_rate = params_rate(params);
>  	unsigned int slot_width = 0;
>  	unsigned int val = 0;
>  	unsigned int bclk;
> @@ -956,11 +962,11 @@ static int cs42l42_pcm_hw_params(struct snd_pcm_substream *substream,
>  		break;
>  	}
>  
> -	ret = cs42l42_pll_config(component, bclk);
> +	ret = cs42l42_pll_config(component, bclk, sample_rate);
>  	if (ret)
>  		return ret;
>  
> -	cs42l42_src_config(component, params_rate(params));
> +	cs42l42_src_config(component, sample_rate);
>  
>  	return 0;
>  }