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SubjectRe: [PATCH] sound: soc: fsl: Do not set DAI sysclk when it is equal to system freq
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Hi Nicolin,

> On Tue, Sep 05, 2017 at 10:35:34AM +0200, Łukasz Majewski wrote:
>
>>> And apparently, we shouldn't set bitclk to 66MHz either. Can
>>> you help to find where this 66MHz comes from?
>
>> 2. int asoc_simple_card_init_dai() @ simple-card-utils.c
>
> Oh, I just searched in the simple-card.c but missed this file.
>
>> In this function (point 2.) the
>> simple_dai->sysclk is set and:
>> snd_soc_dai_set_sysclk(dai, 0, simple_dai->sysclk, 0)
>> which sets frequency to 66 MHz [*].
>>
>> The asoc_simple_card_init_dai() is called in
>> asoc_simple_card_dai_init() @ simple-card.c
>> which is assigned to dai_link->init
>> dai_link->init = asoc_simple_card_dai_init; @ simple_card.c
>>
>> And the sysclk itself is defined at:
>> -------------------------------------
>> dai_props->codec_dai->sysclk, which is used at:a
>
> Why codec_dai? Why not dai_props->cpu_dai->sysclk since we are talking
> about SSI?

This is how the simple-card (simple-sound-card) is written.

>
>> asoc_simple_card_startup(), asoc_simple_card_shutdown() and others
>> functions at simple-card.c
>> It is setup at:
>> asoc_simple_card_parse_clk() @ simple-card-utils.c from macro:
>> #define asoc_simple_card_parse_clk_cpu()
>> And the problem is:
>> -------------------
>>
>> At the
>> asoc_simple_card_parse_clk()
>> we finally go to dts node:
>> /soc/aips-bus@02100000/i2c@021a0000/tfa9879@6C
>
> This tfa9879 should be the CODEC right?

Yes. The tfa9879 is a codec (very simple -> I2S + I2C, mono).

They key point here is the asoc_simple_card_parse_clk() function from
simple-card-utils.c

Please look how the clock is assigned; It first checks for cpu clock,
then for "system-clock-frequency" DTS node and _finally_ looks for
another "child" clock [1], which is the codec attached to I2C.

And from there it takes the 66 MHz CLK:
/soc/aips-bus@02100000/i2c@021a0000/tfa9879@6C



>
>> which has clock from I2C (66 MHz).
>
> You mean I2C scl or I2S sclk?

I2C scl.

>
> -----------------------------------------------------------------
>
> But anyway, I feel very confused here as you have 66MHz clock rate
> (regardless of it purpose) for a codec dai but it's been passed to
> a cpu dai (SSI).

Please look into asoc_simple_card_parse_clk().


My DTS [1] (it is different than other in-tree supported codecs - at
least I did not find similar setup in DTSes):

sound {
compatible = "simple-audio-card";
label = "tfa9879-mono";

simple-audio-card,dai-link {
/* DAC */
format = "i2s";
bitclock-master = <&dailink_master>;
frame-master = <&dailink_master>;

dailink_master: cpu {
sound-dai = <&ssi2>;
};
codec {
sound-dai = <&codec>;
};
};
};


&i2c1 {
clock-frequency = <400000>;
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_i2c1>;
status = "okay";

codec: tfa9879@6C {
#sound-dai-cells = <0>;
compatible = "tfa9879";
reg = <0x6C>;
};
};

&ssi2 {
fsl,mode = "i2s-master";
status = "okay";
};

the ssi2 node is defined in imx6qdl.dtsi file (no changes).

The SOC is IMX6Q.

The TFA9879 is a slave for I2S transmission.


>
>> [*] - I could workaround this problem by setting:
>>
>> system-clock-frequency = <0> in
>>
>> dailink_master: cpu {
>> sound-dai = <&ssi2>;
>> };
>>
>> but this is IMHO even worse hack.... than this patch.
>
> I haven't used simple-card for a while so I forgot how to define
> its DT bindings specifically. But you should assign ssi2 as the
> CPU dai and assign tfa9879 as a CODEC dai.
>


--
Best regards,

Lukasz Majewski

--

DENX Software Engineering GmbH, Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd@denx.de

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