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

[Åukasz Majewski]

Hi Nicolin,

> On Tue, Sep 05, 2017 at 10:35:34AM +0200, Åukasz 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

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