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

[cascardo/linux.git] / Documentation / devicetree / bindings / i2c / i2c-gate.txt

diff --git a/Documentation/devicetree/bindings/i2c/i2c-gate.txt b/Documentation/devicetree/bindings/i2c/i2c-gate.txt
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+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>;
+                       };
+               };
+       };