Added device tree binding documentation for Aspeed I2C busses.

Signed-off-by: Brendan Higgins <brendanhigg...@google.com>
---
Changes for v2:
  - None
Changes for v3:
  - Removed reference to "bus" device tree param
Changes for v4:
  - None
Changes for v5:
  - None
Changes for v6:
  - Replaced the controller property with and interrupt controller, leaving only
    the busses in the I2C documentation.
Changes for v7:
  - Changed clock-frequency to bus-frequency in device tree
Changes for v8:
  - Added multi-master property to device tree
---
 .../devicetree/bindings/i2c/i2c-aspeed.txt         | 48 ++++++++++++++++++++++
 1 file changed, 48 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/i2c/i2c-aspeed.txt

diff --git a/Documentation/devicetree/bindings/i2c/i2c-aspeed.txt 
b/Documentation/devicetree/bindings/i2c/i2c-aspeed.txt
new file mode 100644
index 000000000000..bd6480b19535
--- /dev/null
+++ b/Documentation/devicetree/bindings/i2c/i2c-aspeed.txt
@@ -0,0 +1,48 @@
+Device tree configuration for the I2C busses on the AST24XX and AST25XX SoCs.
+
+Required Properties:
+- #address-cells       : should be 1
+- #size-cells          : should be 0
+- reg                  : address offset and range of bus
+- compatible           : should be "aspeed,ast2400-i2c-bus"
+                         or "aspeed,ast2500-i2c-bus"
+- clocks               : root clock of bus, should reference the APB
+                         clock
+- interrupts           : interrupt number
+- interrupt-parent     : interrupt controller for bus, should reference a
+                         aspeed,ast2400-i2c-ic or aspeed,ast2500-i2c-ic
+                         interrupt controller
+
+Optional Properties:
+- bus-frequency        : frequency of the bus clock in Hz defaults to 100 kHz 
when not
+                 specified
+- multi-master : states that there is another master active on this bus.
+
+Example:
+
+i2c {
+       compatible = "simple-bus";
+       #address-cells = <1>;
+       #size-cells = <1>;
+       ranges = <0 0x1e78a000 0x1000>;
+
+       i2c_ic: interrupt-controller@0 {
+               #interrupt-cells = <1>;
+               compatible = "aspeed,ast2400-i2c-ic";
+               reg = <0x0 0x40>;
+               interrupts = <12>;
+               interrupt-controller;
+       };
+
+       i2c0: i2c-bus@40 {
+               #address-cells = <1>;
+               #size-cells = <0>;
+               #interrupt-cells = <1>;
+               reg = <0x40 0x40>;
+               compatible = "aspeed,ast2400-i2c-bus";
+               clocks = <&clk_apb>;
+               bus-frequency = <100000>;
+               interrupts = <0>;
+               interrupt-parent = <&i2c_ic>;
+       };
+};
-- 
2.13.0.219.gdb65acc882-goog

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