linux-kernel - Re: [PATCH V2 2/5] mfd: add support for AMS AS3722 PMIC

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Date:	Fri, 20 Sep 2013 13:39:30 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Laxman Dewangan <ldewangan@...dia.com>
Cc:	sameo@...ux.intel.com, broonie@...nel.org,
	linus.walleij@...aro.org, akpm@...ux-foundation.org,
	devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
	rtc-linux@...glegroups.com, rob.herring@...xeda.com,
	mark.rutland@....com, pawel.moll@....com, swarren@...dotorg.org,
	rob@...dley.net, ijc+devicetree@...lion.org.uk,
	grant.likely@...aro.org,
	Florian Lobmaier <florian.lobmaier@....com>
Subject: Re: [PATCH V2 2/5] mfd: add support for AMS AS3722 PMIC

> The AMS AS3722 is a compact system PMU suitable for mobile phones,
> tablets etc. It has 4 DC/DC step-down regulators, 3 DC/DC step-down
> controller, 11 LDOs, RTC, automatic battery, temperature and
> over-current monitoring, 8 GPIOs, ADC and wathdog.
> 
> Add mfd core driver for the AS3722 to support core functionality.

<snip>

> +Example:
> +--------
> +ams3722 {
> +	compatible = "ams,as3722";
> +	reg = <0x48>
> +
> +	interrupt-parent = <&intc>;
> +	interrupt-controller;
> +	#interrupt-cells = <2>;
> +
> +	gpio-controller;
> +	#gpio-cells = <2>;
> +
> +	gpio {
> +		/*
> +		 * GPIO related properties
> +		 * Refer document bindings/gpio/gpio-as3722.txt
> +		 */
> +	};
> +
> +	regulators {
> +		/*
> +		 * Regulator related properties
> +		 * Refer document bindings/regulator/as3722-regulator.txt
> +		 */
> +	};
> +};

I still don't think this is the way to go. If you can justify that
these sub-devices require their own node, then they should have a
compatible string. The MFD sub-system will then populate the of_node
for you and you can use/request them in the normal way.

To reiterate, Mark's issue was not the existence of the compatible
string, it was with the existence of the child nodes in general.

Personally I think the device should have sub-nodes. It's how  we
dealt with our DB8500 and AB8500 and it works very well. At the end of
the day these all-in-one chips do house very different devices. I see
no harm in describing them that way. I'm sure other OSes can make use
of the sub-devices in similar ways.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog
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