linux-kernel - Re: [PATCH v3 2/5] ARM: dts: add reference voltage property for MXS LRADC

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Date:	Mon, 22 Jul 2013 20:34:47 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Hector Palacios <hector.palacios@...i.com>
CC:	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
	devicetree-discuss@...ts.ozlabs.org,
	alexandre.belloni@...e-electrons.com, jic23@...nel.org,
	fabio.estevam@...escale.com, marex@...x.de,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Subject: Re: [PATCH v3 2/5] ARM: dts: add reference voltage property for MXS
 LRADC

On 07/22/2013 04:04 PM, Hector Palacios wrote:
> Some LRADC channels have fixed pre-dividers so they can measure
> different voltages at full scale. The reference voltage allows to
> expose a scaling attribute through the IIO sysfs so that a user can
> compute the real voltage out of a measured sample value.

I've said before that I'm not convinced that this is the right way to implement 
this. And considering what Thomas said here 
http://www.mail-archive.com/devicetree-discuss@lists.ozlabs.org/msg36691.html I 
guess I'm not alone with that opinion.

- Lars

>
> Signed-off-by: Hector Palacios <hector.palacios@...i.com>
> Acked-by: Marek Vasut <marex@...x.de>
> Acked-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>
> ---
>   Documentation/devicetree/bindings/staging/iio/adc/mxs-lradc.txt | 9 ++++++++-
>   arch/arm/boot/dts/imx23.dtsi                                    | 4 ++++
>   arch/arm/boot/dts/imx28.dtsi                                    | 4 ++++
>   3 files changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/devicetree/bindings/staging/iio/adc/mxs-lradc.txt b/Documentation/devicetree/bindings/staging/iio/adc/mxs-lradc.txt
> index 4688205..6ec485c 100644
> --- a/Documentation/devicetree/bindings/staging/iio/adc/mxs-lradc.txt
> +++ b/Documentation/devicetree/bindings/staging/iio/adc/mxs-lradc.txt
> @@ -1,9 +1,12 @@
>   * Freescale i.MX28 LRADC device driver
>
>   Required properties:
> -- compatible: Should be "fsl,imx28-lradc"
> +- compatible: "fsl,imx28-lradc", "fsl,imx23-lradc"
>   - reg: Address and length of the register set for the device
>   - interrupts: Should contain the LRADC interrupts
> +- fsl,vref: Reference voltage (in mV) for each LRADC channel. This is the
> +	    maximum voltage that can be measured at full scale in each channel
> +	    considering fixed pre-dividers.
>
>   Optional properties:
>   - fsl,lradc-touchscreen-wires: Number of wires used to connect the touchscreen
> @@ -18,4 +21,8 @@ Examples:
>   		reg = <0x80050000 0x2000>;
>   		interrupts = <10 14 15 16 17 18 19
>   				20 21 22 23 24 25>;
> +		fsl,vref = <1850 1850 1850 1850
> +			    1850 1850 1850 7400
> +			    1850 1850 3700 1850
> +			    3700 1850 1850 7400>
>   	};
> diff --git a/arch/arm/boot/dts/imx23.dtsi b/arch/arm/boot/dts/imx23.dtsi
> index 587ceef..e212902 100644
> --- a/arch/arm/boot/dts/imx23.dtsi
> +++ b/arch/arm/boot/dts/imx23.dtsi
> @@ -430,6 +430,10 @@
>   				compatible = "fsl,imx23-lradc";
>   				reg = <0x80050000 0x2000>;
>   				interrupts = <36 37 38 39 40 41 42 43 44>;
> +				fsl,vref = <1850 1850 1850 1850
> +					    1850 1850 3700 7400
> +					    1850 1850 1850 1850
> +					    1850 1850 1850 7400>;
>   				status = "disabled";
>   			};
>
> diff --git a/arch/arm/boot/dts/imx28.dtsi b/arch/arm/boot/dts/imx28.dtsi
> index 6a8acb0..c1b3724 100644
> --- a/arch/arm/boot/dts/imx28.dtsi
> +++ b/arch/arm/boot/dts/imx28.dtsi
> @@ -865,6 +865,10 @@
>   				reg = <0x80050000 0x2000>;
>   				interrupts = <10 14 15 16 17 18 19
>   						20 21 22 23 24 25>;
> +				fsl,vref = <1850 1850 1850 1850
> +					    1850 1850 1850 7400
> +					    1850 1850 3700 1850
> +					    3700 1850 1850 7400>;
>   				status = "disabled";
>   			};
>
> --
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