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

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Message-ID: <07e54d28-3bbc-aad2-146b-30867c0bc337@denx.de>
Date:   Sun, 3 Sep 2017 16:40:21 +0200
From:   Łukasz Majewski <lukma@...x.de>
To:     Fabio Estevam <fabio.estevam@....com>, Timur Tabi <timur@...i.org>,
        Nicolin Chen <nicoleotsuka@...il.com>,
        Xiubo Li <Xiubo.Lee@...il.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        "festevam@...il.com" <festevam@...il.com>
Cc:     "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sound: soc: fsl: Do not set DAI sysclk when it is equal
 to system freq

Hi Fabio,


> [Sorry for the top-posting]
> 
> 
> The driver currently has:
> 
> 
> /*
> * Hardware limitation: The bclk rate must be
> * never greater than 1/5 IPG clock rate
> */
> if (freq * 5 > clk_get_rate(ssi_private->clk)) {
> dev_err(cpu_dai->dev, "bitclk > ipgclk/5\n");
> return -EINVAL;
> }
> 

Unfortunately not.

This is the part of fsl_ssi_set_bclk() function which is called after 
fsl_ssi_set_dai_sysclk() (which sets ssi_private->bitclk_freq = freq;).

Before the aforementioned check we do have:

	if (ssi_private->bitclk_freq)
		freq = ssi_private->bitclk_freq;
	else
		freq = params_channels(hw_params) * 32 * 	params_rate(hw_params);


Which assigns freq = bitclk_freq (66 MHz)

And then we break on this particular check:

66MHz * 5 > 66 MHz.



The culprit IMHO is the  ssi_private->bitclk_freq = freq; in the 
fsl_ssi_set_dai_sysclk(), since we _should_ set SSI's IP block clock 
(ssi_private->clk), not the bit clock (BCLK).


This patch just quits early if it detects change, which don't need to be 
done.

> 
> Isn't this properly taking care of the clock restriction?
> 
> ________________________________
> From: Lukasz Majewski <lukma@...x.de>
> Sent: Sunday, September 3, 2017 8:05:01 AM
> To: Timur Tabi; Nicolin Chen; Xiubo Li; Fabio Estevam; Liam Girdwood; Mark Brown; Jaroslav Kysela; Takashi Iwai
> Cc: alsa-devel@...a-project.org; linuxppc-dev@...ts.ozlabs.org; linux-kernel@...r.kernel.org; Lukasz Majewski
> Subject: [PATCH] sound: soc: fsl: Do not set DAI sysclk when it is equal to system freq
> 
> 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].
> 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].
> 
> 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
> 
> 


-- 
Best regards,

Lukasz Majewski

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