linux-kernel - Re: [PATCH 5/5] ARM: dts: exynos4412-trats2: Add ADC's dt data to get temperature of SoC/battery

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Message-id: <531F0AEC.7010606@samsung.com>
Date:	Tue, 11 Mar 2014 14:09:00 +0100
From:	Tomasz Figa <t.figa@...sung.com>
To:	Chanwoo Choi <cw00.choi@...sung.com>, kgene.kim@...sung.com
Cc:	linux-samsung-soc@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, kyungmin.park@...sung.com,
	rob.herring@...xeda.com, pawel.moll@....com, mark.rutland@....com,
	swarren@...dotorg.org, ijc+devicetree@...lion.org.uk,
	linux@....linux.org.uk
Subject: Re: [PATCH 5/5] ARM: dts: exynos4412-trats2: Add ADC's dt data to get
 temperature of SoC/battery

Hi Chanwoo,

On 11.03.2014 08:54, Chanwoo Choi wrote:
> This patch use ADC to get the temperature of SoC/battery by using NTC thermistor
> driver in hwmon. NTC thermistor driver covnvert ADC's raw data to temperature
> by using following variables:
>
> - pullup-uv    : Voltage
> - pullup-ohm   : Pull-up resistance
> - pulldown-ohm : Pull-down resistance
> - io-channels  : It means ADC channel.
>

Those properties are well-defined in "ntc,ncp15wb473" DT bindings 
documentation. There is no need to repeat them here.

> Signed-off-by: Chanwoo Choi <cw00.choi@...sung.com>
> ---
>   arch/arm/boot/dts/exynos4412-trats2.dts | 21 +++++++++++++++++++++
>   1 file changed, 21 insertions(+)
>
> diff --git a/arch/arm/boot/dts/exynos4412-trats2.dts b/arch/arm/boot/dts/exynos4412-trats2.dts
> index 4f851cc..fc517c3 100644
> --- a/arch/arm/boot/dts/exynos4412-trats2.dts
> +++ b/arch/arm/boot/dts/exynos4412-trats2.dts
> @@ -106,6 +106,27 @@
>   		};
>   	};
>
> +	adc: adc@...C0000 {
> +		vdd-supply = <&ldo3_reg>;
> +		status = "okay";
> +
> +		ncp15wb473@0 {

style: Nodes should have generic names, e.g. thermistor@0.

Also if node name is suffixed with @unit-address, then the node should 
have a reg property with its first entry corresponding to the 
unit-address. Now there is no physical unit-address definition for those 
thermistors, so they shouldn't use this naming pattern, but rather 
something like "thermistor-0" or "thermistor-ap".

> +			compatible = "ntc,ncp15wb473";
> +			pullup-uv = <1800000>;	 /* VCC_1.8V_AP */
> +			pullup-ohm = <100000>;	 /* 100K */
> +			pulldown-ohm = <100000>; /* 100K */
> +			io-channels = <&adc 1>;  /* AP temperature */
> +		};
> +
> +		ncp15wb473@1 {
> +			compatible = "ntc,ncp15wb473";
> +			pullup-uv = <1800000>;	 /* VCC_1.8V_AP */
> +			pullup-ohm = <100000>;	 /* 100K */
> +			pulldown-ohm = <100000>; /* 100K */
> +			io-channels = <&adc 2>;  /* Battery temperature */
> +		};

Anyway, I don't think it is correct to place IIO consumers under IIO 
provider node, because IIO is not a control bus, but rather a resource 
provider, like GPIO, clock, etc. So both thermistor nodes should be 
placed outside the adc node. (They might be grouped in a simple-bus 
subnode, though, to improve readability.)

Best regards,
Tomasz
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