arm64: hi6220: Document devicetree bindings for Hisilicon hi6220 SoC

This patch adds documentation for the devicetree bindings used by the
DT files of Hisilicon hi6220 SoC mobile platform.
Signed-off-by: Bintian Wang <bintian.wang@huawei.com>
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Haojian Zhuang <haojian.zhuang@linaro.org>
Acked-by: Stephen Boyd <sboyd@codeaurora.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>

Documentation/devicetree/bindings/arm/hisilicon/hisilicon.txt

 Hisilicon Platforms Device Tree Bindings
 ----------------------------------------------------
+Hi6220 SoC
+Required root node properties:
+	- compatible = "hisilicon,hi6220";
 
 Hi4511 Board
 Required root node properties:
@@ -13,6 +16,9 @@ HiP01 ca9x2 Board
 Required root node properties:
 	- compatible = "hisilicon,hip01-ca9x2";
 
+HiKey Board
+Required root node properties:
+	- compatible = "hisilicon,hi6220-hikey", "hisilicon,hi6220";
 
 Hisilicon system controller
 
@@ -40,6 +46,87 @@ Example:
 		reboot-offset = <0x4>;
 	};
 
+-----------------------------------------------------------------------
+Hisilicon Hi6220 system controller
+
+Required properties:
+- compatible : "hisilicon,hi6220-sysctrl"
+- reg : Register address and size
+- #clock-cells: should be set to 1, many clock registers are defined
+  under this controller and this property must be present.
+
+Hisilicon designs this controller as one of the system controllers,
+its main functions are the same as Hisilicon system controller, but
+the register offset of some core modules are different.
+
+Example:
+	/*for Hi6220*/
+	sys_ctrl: sys_ctrl@f7030000 {
+		compatible = "hisilicon,hi6220-sysctrl", "syscon";
+		reg = <0x0 0xf7030000 0x0 0x2000>;
+		#clock-cells = <1>;
+	};
+
+
+Hisilicon Hi6220 Power Always ON domain controller
+
+Required properties:
+- compatible : "hisilicon,hi6220-aoctrl"
+- reg : Register address and size
+- #clock-cells: should be set to 1, many clock registers are defined
+  under this controller and this property must be present.
+
+Hisilicon designs this system controller to control the power always
+on domain for mobile platform.
+
+Example:
+	/*for Hi6220*/
+	ao_ctrl: ao_ctrl@f7800000 {
+		compatible = "hisilicon,hi6220-aoctrl", "syscon";
+		reg = <0x0 0xf7800000 0x0 0x2000>;
+		#clock-cells = <1>;
+	};
+
+
+Hisilicon Hi6220 Media domain controller
+
+Required properties:
+- compatible : "hisilicon,hi6220-mediactrl"
+- reg : Register address and size
+- #clock-cells: should be set to 1, many clock registers are defined
+  under this controller and this property must be present.
+
+Hisilicon designs this system controller to control the multimedia
+domain(e.g. codec, G3D ...) for mobile platform.
+
+Example:
+	/*for Hi6220*/
+	media_ctrl: media_ctrl@f4410000 {
+		compatible = "hisilicon,hi6220-mediactrl", "syscon";
+		reg = <0x0 0xf4410000 0x0 0x1000>;
+		#clock-cells = <1>;
+	};
+
+
+Hisilicon Hi6220 Power Management domain controller
+
+Required properties:
+- compatible : "hisilicon,hi6220-pmctrl"
+- reg : Register address and size
+- #clock-cells: should be set to 1, some clock registers are define
+  under this controller and this property must be present.
+
+Hisilicon designs this system controller to control the power management
+domain for mobile platform.
+
+Example:
+	/*for Hi6220*/
+	pm_ctrl: pm_ctrl@f7032000 {
+		compatible = "hisilicon,hi6220-pmctrl", "syscon";
+		reg = <0x0 0xf7032000 0x0 0x1000>;
+		#clock-cells = <1>;
+	};
+
 -----------------------------------------------------------------------
 Hisilicon HiP01 system controller