linux-kernel - Re: [PATCH 7/8] ASoC: atmel: document clock properties of the wm8904 driver

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Message-ID: <532A5481.6000008@atmel.com>
Date:	Thu, 20 Mar 2014 10:37:53 +0800
From:	Bo Shen <voice.shen@...el.com>
To:	Mark Brown <broonie@...nel.org>
CC:	<nicolas.ferre@...el.com>,
	Boris BREZILLON <b.brezillon@...rkiz.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	"Mark Rutland" <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Rob Landley <rob@...dley.net>, <devicetree@...r.kernel.org>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 7/8] ASoC: atmel: document clock properties of the wm8904
 driver

Hi Mark,

On 03/19/2014 06:28 PM, Mark Brown wrote:
> On Wed, Mar 19, 2014 at 01:57:23PM +0800, Bo Shen wrote:
>> On 03/17/2014 07:55 PM, Mark Brown wrote:
>
>>> If this is a clock for the CODEC it should be documented as part of the
>>> binding for the CODEC and connected to the CODEC in the device tree
>>> rather than being part of a machine driver binding.
>
>> This is a optional clock for CODEC which depends on hardware design. There
>> are 3 options for this clock, wm8904 as an example.
>> 1. Using internal FLL, so won't use this clock.
>> 2. Using external oscillator, no need to retrieve this clock.
>> 3. Using SoC provide this clock (we use this case).
>
>> After considering these 3 options, if we put this into CODEC driver to do
>> it, I think it will be more complicate to do logic judgement. Do you think
>> so?
>
> There shouldn't be any meaningful complexity from the above cases -
> cases 2 and 3 are the same and if the clock isn't used at all then it
> can be omitted.  If the FLL is clocked from MCLK then the CODEC driver
> should be able to work out how to configure it easily, the device isn't
> like a digital hub CODEC with lots of clocking options.

For this, in my mind, I think we need add following parameters in DT.
1. sysclk_src_from_fll --> we need do nothing.
2. sysclk_src_from_mclk
    2.1 use_external_xtal --> we need clock_frequency
    2.2 !use_external_xtal --> we need retrieve clock and clock_frequency.

So, the dt may looks like:
for case 1:
wm8904: wm8904@1a {
	reg = <0x1a>;
	sysclk_src_from_fll;
}

for case 2.1:
wm8904: wm8904@1a {
	reg = <0x1a>;
	sysclk_src_from_mclk;
	use_external_xtal;
	clock_frequency = 12000000;
}

for case 2.2:
wm8904: wm8904@1a {
	reg = <0x1a>;
	sysclk_src_from_mclk;
	clocks = <&pck0>;
	clock-names = "mclk";
	clock_frequency = 32768;
}

Does this acceptable? Or any other better suggestion for this?

Best Regards,
Bo Shen

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