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Date:	Mon, 21 Jul 2014 10:52:28 +0900
From:	Chanwoo Choi <cw00.choi@...sung.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Chanwoo Choi <cwchoi00@...il.com>, jic23@...nel.org,
	naveen krishna <ch.naveen@...sung.com>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Rob Herring <robh+dt@...nel.org>, pawel.moll@....com,
	Mark Rutland <mark.rutland@....com>,
	ijc+devicetree@...lion.org.uk, Kumar Gala <galak@...eaurora.org>,
	rdunlap@...radead.org, Kyungmin Park <kyungmin.park@...sung.com>,
	Tomasz Figa <t.figa@...sung.com>, linux-iio@...r.kernel.org,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	devicetree <devicetree@...r.kernel.org>,
	linux-doc@...r.kernel.org
Subject: Re: [PATCHv6 3/4] iio: devicetree: Add DT binding documentation for
 Exynos3250 ADC

On 07/19/2014 03:48 AM, Arnd Bergmann wrote:
> On Saturday 19 July 2014 02:02:09 Chanwoo Choi wrote:
>> On Sat, Jul 19, 2014 at 1:33 AM, Arnd Bergmann <arnd@...db.de> wrote:
>>> On Saturday 19 July 2014 01:23:15 Chanwoo Choi wrote:
>>>> If don't add new compatible including specific exynos version,
>>>> I would add new 'adc-needs-sclk' property with existing 'exynos-adc-v2'
>>>> compatible name.
> 
> What I actually meant is using compatible="exynos-adc-v2.1" or similar
> rather than "exynos3250-adc". However, as you already explained, the
> version numbers are apparently just made up, so using "exynos3250-adc"
> is actually better here. If a future exynos7890 uses the same clocks
> as exynos3250, it can simply use the same "exynos3250-adc" string here.

OK, I'll use "exynos3250-adc" compatible string instead of "exynos3250-adc-v2".

> 
>>>> Dear Naveen, Tomasz,
>>>>
>>>> If existing exynos-adc driver add just one property for 'sclk_adc'
>>>> as following, exynos-adc could not include the exynos version
>>>> in compatible name.
>>>>
>>>> I need your opinion about it.
>>>>
>>>>                 adc: adc@...C0000 {
>>>>                         compatible = "samsung,exynos-adc-v2";
>>>>                         reg = <0x126C0000 0x100>, <0x10020718 0x4>;
>>>>                         interrupts = <0 137 0>;
>>>>                         clock-names = "adc", "sclk_adc";
>>>>                         clocks = <&cmu CLK_TSADC>, <&cmu CLK_SCLK_TSADC>;
>>>> +                        adc-needs-sclk;
>>>>                         #io-channel-cells = <1>;
>>>>                         io-channel-ranges;
>>>>                 }
>>>
>>> How about just making it an optional clock? That would be much
>>> easier because then you can simply see if the clock itself is
>>> there and use it, or otherwise ignore it.
>>
>> The v1 of this patchset[1] got the clock of 'sclk_adc'  but if the dt node
>> of ADC in dtsi file didn't include 'sclk_adc', print just warning message
>> without stopping probe as following:
>>
>>  [1] https://lkml.org/lkml/2014/4/10/710
>>
>> +       info->sclk = devm_clk_get(&pdev->dev, "sclk_adc");
>> +       if (IS_ERR(info->sclk)) {
>> +               dev_warn(&pdev->dev, "failed getting sclk clock, err = %ld\n",
>> +                                                       PTR_ERR(info->sclk));
>> +               info->sclk = NULL;
>> +       }
>>
>> But, Tomasz Figa suggested the method[2] of this patchset(v6).
>>  [2] https://lkml.org/lkml/2014/4/11/189
> 
> Yes, your current version is certainly better than this, but another way
> to address Tomasz' comment would be to change the binding to list the "sclk"
> as optional for any device and make the code silently ignore missing sclk
> entries, like:
> 
> 
> 	info->sclk = devm_clk_get(&pdev->dev, "sclk");
> 	if (IS_ERR(info->sclk)) {
> 		switch (PTR_ERR(info->sclk)) {
> 		case -EPROBE_DEFER:
> 			/* silently return error so we can retry */
> 			return -EPROBE_DEFER:
> 		case -ENOENT:
> 			/* silently ignore missing optional clk */
> 			info->sclk = NULL;
> 			break;
> 		default:
> 			/* any other error: clk is defined by doesn't work  */
> 			dev_err(&pdev->dev, "failed getting sclk clock, err = %ld\n",
> 				PTR_ERR(info->sclk));
> 			return PTR_ERR(info->sclk));
> 		}
> 	}

I tested this patch suggested by you.
But, devm_clk_get returns always '-ENOENT' on follwong two cases:

Case 1.
ADC dt node in exynos3250.dtsi don't include 'sclk' clock as following:

                adc: adc@...C0000 {
                        compatible = "samsung,exynos3250-adc";
                        reg = <0x126C0000 0x100>, <0x10020718 0x4>;
                        interrupts = <0 137 0>;
                        clock-names = "adc";
                        clocks = <&cmu CLK_TSADC>;
                        #io-channel-cells = <1>;
                        io-channel-ranges;
		};

Case 2.
ADC dt node in exynos3250.dtsi don't include 'sclk' clock
but, exynos3250 clock controller don't support CLK_SCLK_TSADC clock as following:

                adc: adc@...C0000 {
                        compatible = "samsung,exynos3250-adc";
                        reg = <0x126C0000 0x100>, <0x10020718 0x4>;
                        interrupts = <0 137 0>;
                        clock-names = "adc", "sclk";
                        clocks = <&cmu CLK_TSADC>, <&cmu CLK_SCLK_TSADC>;
                        #io-channel-cells = <1>;
                        io-channel-ranges;
		};


So, I think exynos-adc needs to use 'needs_sclk' field suggested by Tomasz Figa.

> 
> One more comment about the name: Both in the code you use "sclk" as the
> name, so presumably that is the actual name of the clk as known to this
> driver, and it makes sense to use clock-names="sclk" as well, if you want
> to have any name.

OK, I'll use 'sclk' clock name for special clock of ADC.

Thanks,
Chanwoo Choi
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