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

From: Rhyland Klein
Date: Fri Feb 22 2013 - 17:05:26 EST

On 2/22/2013 2:46 PM, Stephen Warren wrote:
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)?

+ 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>;
+ };

The "connection" between supplier and supplies isn't really a hard connection.
Essentially, the core code uses the names/nodes in the list and iterates over
all the power_supplies that are registered and does matching.

I don't have any experience working with a single node that would spawn multiple
supplies, though the situation I am sure is possible. I am interested to see what
the consensus is around this design for multiple supplies, as I don't have a
preference either way.



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