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

Hi Nicolin,

On Wed, Sep 06, 2017 at 11:22:48AM +0200, Łukasz Majewski wrote:

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Here is the routine that I understood from the code:
1) asoc_simple_card_parse_clk_cpu(dev, cpu, dai_link, cpu_dai);
    => asoc_simple_card_parse_clk(dev, cpu,        // cpu node in sound{} [1]
		   		 dai_link->cpu_of_node,     // node ssi2 [2]
				 cpu_dai, dai_link->cpu_dai_name);
    ==> 1.1) devm_get_clk_from_child(dev, node, NULL);                 // [1]
    ==> 1.2) of_property_read_u32(node, "system-clock-frequency", &val)// [1]
    ==> 1.3) devm_get_clk_from_child(dev, dai_of_node, NULL);          // [2]

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For the cpu routine, it first checks for clock property under cpu
node of simple-card, then for "system-clock-frequency" in the cpu
node of simple-card, and finally looks for clock property in ssi2
node.

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-----> dev: sound
-----> clk node: /soc/aips-bus@02000000/spba-bus@02000000/ssi@0202c000
-----> Clk asignment

And this clock is taken from this node. It looks like ipg clock for ssi...

This makes sense now. The devm_get_clk_from_child() in 1.3) fetched
the first clock of ssi2 -- ipg clock.

Yes, exactly (for SSI2) [1]:

	clocks = <&clks IMX6QDL_CLK_SSI2_IPG>,
		 <&clks IMX6QDL_CLK_SSI2>;
	clock-names = "ipg", "baud";

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The problem is with the "lack" of clock nodes/properties at

  			dailink_master: cpu {
  			    sound-dai = <&ssi2>;
			    clock = <&SSSS>;

	If possible I do prefer a solution, which uses only DTS.
	
Side question - how to refer to baud clock from [1]?

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			    system-clock-frequency = <XXXX>;
  			};

This is the right solution based on current simple-card driver. For
SSI (having two clocks), you have to specify the baud clock in the
cpu node like that. I believe this is what the simple-card designer
expected users to do since the cpu node is the first place that the
driver tries to look at.

I will give a shoot the option with adding the ipg clock.

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I think that the proper solution would be to add check for:

freq < sysclk/5 in fsl_ssi_set_dai_sysclk() and return -ENOTSUPP to
make the simple-audo-card driver happy (and not introducing
regressions).

As I said in the first place, adding another check in set_sysclk()
is not that essential but seems to be plausible to me. So I am okay
if you really want to have that.

Thanks for help.

-- 
Best regards,

Lukasz Majewski

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