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

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Date:   Tue, 5 Sep 2017 10:19:05 +0200
From:   Łukasz Majewski <lukma@...x.de>
To:     Nicolin Chen <nicoleotsuka@...il.com>
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 09/05/2017 09:52 AM, Nicolin Chen wrote:
> On Tue, Sep 05, 2017 at 09:37:43AM +0200, Łukasz Majewski wrote:
> 
>>>> 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.
>>
>> Yes, exactly.
>>
>> In my case the bclk is set to ipg clock, which is the SSI IP block clock
>> (ipg).
> 
> Can you elaborate why you set ipg clock as bclk? I don't remember SSI could
> derive bitclock from ipg clock.

Just to be clear:

What clock shall be set with:

struct snd_soc_dai_ops {

	int (*set_sysclk)(struct snd_soc_dai *dai,
		int clk_id, unsigned int freq, int dir);
}

callback?

The SSI IP block or BCLK ?


> 
>>>> 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.
>>
>> I think that this clock is not changing for the SoC. It should be 66 MHz
>> fixed.
> 
> What I mean is that we cannot just look at this SoC. Today is 66MHz for this
> SoC. Tomorrow could be 133MHz for another one. We should put a check that none
> of these shall pass -- the 1/5 limit.
> 

Ok. Good point.


-- 
Best regards,

Lukasz Majewski

--

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