linux-kernel - Re: [PATCH] sound: soc: fsl: Do not set DAI sysclk when it is equal to system freq

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Date:   Mon, 4 Sep 2017 22:06:03 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Lukasz Majewski <lukma@...x.de>
Cc:     Timur Tabi <timur@...i.org>, Xiubo Li <Xiubo.Lee@...il.com>,
        Fabio Estevam <fabio.estevam@....com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, alsa-devel@...a-project.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sound: soc: fsl: Do not set DAI sysclk when it is equal
 to system freq

On Sun, Sep 03, 2017 at 01:05:01PM +0200, Lukasz Majewski wrote:
> The problem is visible in the following setup (on the imx6q):
> "simple-audio-card" -> ssi2 -> I2S + I2C -> codec
> 
> The function call log (simple-card probe -> CONFIG_SND_SIMPLE_CARD):
> 
> asoc_simple_card_init_dai() @ sound/soc/generic/simple-card-utils.c
> snd_soc_dai_set_sysclk()
> fsl_ssi_set_dai_sysclk() @ sound/soc/fsl/fsl_ssi.c
> 
> The last call is changing the bit clock (BCLK) frequency to SSI's IP
> block clock (ipg = 66 MHz) [1].

I think a bigger question here is why the routine sets BCLK to 66MHz.

> This is wrong, since IMX SSI block requires the I2S BCLK to be less
> than 1/5 of [1].
> 
> As a result the driver initialization passes without any errors, but the
> speaker-test test case breaks.
> 
> This commit checks if the fsl_ssi_set_dai_sysclk() frequency passed is
> not equal to [1].

I don't feel it's quite comprehensive...what if it's being set to 67MHz.

Thanks
Nicolin

> Signed-off-by: Lukasz Majewski <lukma@...x.de>
> ---
>  sound/soc/fsl/fsl_ssi.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/sound/soc/fsl/fsl_ssi.c b/sound/soc/fsl/fsl_ssi.c
> index 173cb84..1186fa9 100644
> --- a/sound/soc/fsl/fsl_ssi.c
> +++ b/sound/soc/fsl/fsl_ssi.c
> @@ -809,6 +809,8 @@ static int fsl_ssi_set_dai_sysclk(struct snd_soc_dai *cpu_dai,
>  		int clk_id, unsigned int freq, int dir)
>  {
>  	struct fsl_ssi_private *ssi_private = snd_soc_dai_get_drvdata(cpu_dai);
> +	if (clk_get_rate(ssi_private->clk) == freq)
> +		return 0;
>  
>  	ssi_private->bitclk_freq = freq;
>  
> -- 
> 2.1.4
>