i2c: rcar: add compatible entry for r8a7791

While we are here, also brush up the devicetree binding documentation.
The example was an inappropriate copy from the sh_mobile driver.
Signed-off-by: Wolfram Sang <wsa@sang-engineering.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

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

@@ -6,6 +6,7 @@ Required properties:
 	"renesas,i2c-r8a7778"
 	"renesas,i2c-r8a7779"
 	"renesas,i2c-r8a7790"
+	"renesas,i2c-r8a7791"
 - reg: physical base address of the controller and length of memory mapped
   region.
 - interrupts: interrupt specifier.
@@ -13,11 +14,16 @@ Required properties:
 Optional properties:
 - clock-frequency: desired I2C bus clock frequency in Hz. The absence of this
   propoerty indicates the default frequency 100 kHz.
+- clocks: clock specifier.
 
 Examples :
 
-i2c0: i2c@e6500000 {
-	compatible = "renesas,i2c-rcar-h2";
-	reg = <0 0xe6500000 0 0x428>;
-	interrupts = <0 174 0x4>;
+i2c0: i2c@e6508000 {
+	#address-cells = <1>;
+	#size-cells = <0>;
+	compatible = "renesas,i2c-r8a7791";
+	reg = <0 0xe6508000 0 0x40>;
+	interrupts = <0 287 IRQ_TYPE_LEVEL_HIGH>;
+	clocks = <&mstp9_clks R8A7791_CLK_I2C0>;
+	clock-frequency = <400000>;
 };

drivers/i2c/busses/i2c-rcar.c

@@ -638,6 +638,7 @@ static const struct of_device_id rcar_i2c_dt_ids[] = {
 	{ .compatible = "renesas,i2c-r8a7778", .data = (void *)I2C_RCAR_GEN1 },
 	{ .compatible = "renesas,i2c-r8a7779", .data = (void *)I2C_RCAR_GEN1 },
 	{ .compatible = "renesas,i2c-r8a7790", .data = (void *)I2C_RCAR_GEN2 },
+	{ .compatible = "renesas,i2c-r8a7791", .data = (void *)I2C_RCAR_GEN2 },
 	{},
 };
 MODULE_DEVICE_TABLE(of, rcar_i2c_dt_ids);