dt-bindings: i2c: add support for 'i2c-gate' subnode

Handle i2c gates similarly to how i2c arbitrators are handled.
This gets rid of a pointless 'reg' property for i2c gates.

I.e. this new and more compact style

some-gate {
i2c-gate {
#address-cells = <1>;
#size-cells = <0>;

some-i2c-device@50 {
reg = <0x50>;
};
};
};

instead of the old

some-gate {
#address-cells = <1>;
#size-cells = <0>;

i2c@0 {
reg = <0>;

#address-cells = <1>;
#size-cells = <0>;

some-i2c-device@50 {
reg = <0x50>;
};
};
};

Acked-by: Rob Herring <[e-mail]>
Reviewed-by: Wolfram Sang <[e-mail]>
Signed-off-by: Peter Rosin <[e-mail]>

Documentation/devicetree/bindings/i2c/i2c-gate.txt

···
+An i2c gate is useful to e.g. reduce the digital noise for RF tuners connected
+to the i2c bus. Gates are similar to arbitrators in that you need to perform
+some kind of operation to access the i2c bus past the arbitrator/gate, but
+there are no competing masters to consider for gates and therefore there is
+no arbitration happening for gates.
+
+Common i2c gate properties.
+
+- i2c-gate child node
+
+Required properties for the i2c-gate child node:
+- #address-cells = <1>;
+- #size-cells = <0>;
+
+Optional properties for i2c-gate child node:
+- Child nodes conforming to i2c bus binding
+
+
+Example :
+
+	/*
+	   An Invensense mpu9150 at address 0x68 featuring an on-chip Asahi
+	   Kasei ak8975 compass behind a gate.
+	 */
+
+	mpu9150@68 {
+		compatible = "invensense,mpu9150";
+		reg = <0x68>;
+		interrupt-parent = <&gpio1>;
+		interrupts = <18 1>;
+
+		i2c-gate {
+			#address-cells = <1>;
+			#size-cells = <0>;
+
+			ax8975@c {
+				compatible = "ak,ak8975";
+				reg = <0x0c>;
+			};
+		};
+	};

MAINTAINERS

···
 F:	Documentation/i2c/muxes/
 F:	Documentation/devicetree/bindings/i2c/i2c-mux*
 F:	Documentation/devicetree/bindings/i2c/i2c-arb*
+F:	Documentation/devicetree/bindings/i2c/i2c-gate*
 F:	drivers/i2c/i2c-mux.c
 F:	drivers/i2c/muxes/
 F:	include/linux/i2c-mux.h