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

This gets rid of the need for a pointless 'reg' property for i2c
arbitrators.

I.e. this new and more compact style

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

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

instead of the old

	some-arbitrator {
		#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 <robh@kernel.org>
Reviewed-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Peter Rosin <peda@axentia.se>

1 files changed, 35 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/i2c/i2c-arb.txt b/Documentation/devicetree/bindings/i2c/i2c-arb.txt
new file mode 100644
index 000000000000..59abf9277bdc
--- /dev/null
+++ b/Documentation/devicetree/bindings/i2c/i2c-arb.txt
@@ -0,0 +1,35 @@
+Common i2c arbitration bus properties.
+
+- i2c-arb child node
+
+Required properties for the i2c-arb child node:
+- #address-cells = <1>;
+- #size-cells = <0>;
+
+Optional properties for i2c-arb child node:
+- Child nodes conforming to i2c bus binding
+
+
+Example :
+
+	/*
+	   An NXP pca9541 I2C bus master selector at address 0x74
+	   with a NXP pca8574 GPIO expander attached.
+	 */
+
+	arb@74 {
+		compatible = "nxp,pca9541";
+		reg = <0x74>;
+
+		i2c-arb {
+			#address-cells = <1>;
+			#size-cells = <0>;
+
+			gpio@38 {
+				compatible = "nxp,pca8574";
+				reg = <0x38>;
+				#gpio-cells = <2>;
+				gpio-controller;
+			};
+		};
+	};