linux-kernel - Re: Please suggest proper format for DT properties.

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Date:	Tue, 22 Sep 2015 10:36:51 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Constantine Shulyupin <const@...elinux.com>,
	Jean Delvare <jdelvare@...e.com>
Cc:	open list <linux-kernel@...r.kernel.org>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
	<devicetree@...r.kernel.org>, Guenter Roeck <linux@...ck-us.net>,
	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>
Subject: Re: Please suggest proper format for DT properties.

On Saturday 19 September 2015 01:36:43 Constantine Shulyupin wrote:
> 
> I am designing DT support for a hwmon chip. 
> It has some sensors, each of them can be:
>  - "disabled"
>  - "thermal diode"
>  - "thermistor"
>  - "voltage"
> 
> Four possible options for DT properties format.
> 
> Option 1: Separated property for each sensor.
> 
> Example nct7802 node:
> 
> nct7802 {
>         compatible = "nuvoton,nct7802";
>         reg = <0x2a>;
>         nuvoton,sensor1-type = "thermistor";
>         nuvoton,sensor2-type = "disabled";
>         nuvoton,sensor3-type = "voltage";
> };
> 
> Option 2: Array of strings for all sensors.
> 
> nct7802 {
>         compatible = "nuvoton,nct7802";
>         reg = <0x2a>;
>         nuvoton,sensors-types = "thermistor", "disabled", "voltage";
> };
> 
> Option 3: Sets of 4 cells.
> 
>   Borrowed from marvell,reg-init and broadcom,c45-reg-init.
> 
>   The first cell is the page address, 
>   the second a register address within the page,
>   the third cell contains a mask to be ANDed with the existing register
>   value, and the fourth cell is ORed with the result to yield the
>   new register value. If the third cell has a value of zero,
>   no read of the existing value is performed.
> 
> Example nct7802 node:
> 
> nct7802 {
>         compatible = "nuvoton,nct7802";
>         reg = <0x2a>;
>         nct7802,reg-init =
>                 <0 0x21 0 0x01 > // START = 1
>                 <0 0x22 0x03 0x02>; // RTD1_MD = 2
> };
> 

I would strongly prefer Option 1 or 2 over option 3.
Between 1 and 2, I'd probably go for 1. Another option might
be to have a subnode per sensor:

nct7802@2a {
        compatible = "nuvoton,nct7802";
        reg = <0x2a>;
	#address-cells=<1>;
	#size-cells=<0>;

	sensor@1 {
		compatible = "nuvoton,nct7802-thermistor";
		further-properties;
	};
	sensor@3 {
		compatible = "nuvoton,nct7802-voltage";
		for-example-range-mv = <0 5000>;
	};
};

In either case, I'd say that disabled sensors should not need to
be listed.

	Arnd
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