linux-kernel - Re: [RFC v2 1/3] power_supply: Define Binding for supplied-nodes

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Date:	Fri, 22 Feb 2013 12:46:01 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Rhyland Klein <rklein@...dia.com>
CC:	Anton Vorontsov <cbou@...l.ru>,
	David Woodhouse <dwmw2@...radead.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <rob.herring@...xeda.com>,
	linux-tegra@...r.kernel.org, devicetree-discuss@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Subject: Re: [RFC v2 1/3] power_supply: Define Binding for supplied-nodes

On 02/21/2013 04:11 PM, Rhyland Klein wrote:
> This property is meant to be used in device nodes which represent
> power_supply devices that wish to provide a list of supplies to
> which they provide power. A common case is a AC Charger with
> the batteries it powers.

> diff --git a/Documentation/devicetree/bindings/power_supply/power_supply.txt b/Documentation/devicetree/bindings/power_supply/power_supply.txt

> +Optional Properties:
> + - power-supply : This property is added to a supply in order to list the
> +   devices which supply it power, referenced by their phandles.

DT properties that reference resources are usually named in the plural,
so "power-supplies" would be more appropriate here.

It seems plausible that a single DT node could represent/instantiate
multiple separate supply objects. I think we want to employ the standard
pattern of <phandle args*> rather than just <phandle>.

That way, each supply that can supply others would have something like a
#supply-cells = <n>, where n is the number of cells that the supply uses
to name the multiple supplies provided by that node. 0 would be a common
value here. 1 might be used for a node that represents many supplies.

When a client supply uses a providing supply as the supply(!), do you
need any flags to parameterize the connection? If so, that might be
cause for a supplier to have a larger #supply-cells, so the flags could
be represented.

That all said, regulators assume 1 node == 1 regulator, so an
alternative would be for a multi-supply node to include a child node per
supply, e.g.:

power@xxx {
    ...
    supply1 {
        ...
    };
    supply2 {
        ...
    };
};

client {
    supplies = <&supply1> <&supply2>;
};

I don't recall why regulators went for the style above rather than the
#supply-cells style. Cc Mark Brown for any comment here.

Also, do supplies and regulators need to inter-operate in any way (e.g.
reference each-other in DT)?

> +Example:
> +
> +	usb-charger: power@e {
> +		compatible = "some,usb-charger";
> +		...
> +	};
> +
> +	ac-charger: power@e {
> +		compatible = "some,ac-charger";
> +		...
> +	};
> +
> +	battery@b {
> +		compatible = "some,battery";
> +		...
> +		power-supply = <&usb-charger>, <&ac-charger>;
> +	};

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