dt-bindings: add documentation for s3c2410 clock controller

Describe the clock controller of s3c2410, s3c2440 and s3c2442.
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>

Documentation/devicetree/bindings/clock/samsung,s3c2410-clock.txt

+* Samsung S3C2410 Clock Controller
+
+The S3C2410 clock controller generates and supplies clock to various controllers
+within the SoC. The clock binding described here is applicable to the s3c2410,
+s3c2440 and s3c2442 SoCs in the s3c24x family.
+
+Required Properties:
+
+- compatible: should be one of the following.
+  - "samsung,s3c2410-clock" - controller compatible with S3C2410 SoC.
+  - "samsung,s3c2440-clock" - controller compatible with S3C2440 SoC.
+  - "samsung,s3c2442-clock" - controller compatible with S3C2442 SoC.
+- reg: physical base address of the controller and length of memory mapped
+  region.
+- #clock-cells: should be 1.
+
+Each clock is assigned an identifier and client nodes can use this identifier
+to specify the clock which they consume. Some of the clocks are available only
+on a particular SoC.
+
+All available clocks are defined as preprocessor macros in
+dt-bindings/clock/samsung,s3c2410-clock.h header and can be used in device
+tree sources.
+
+External clocks:
+
+The xti clock used as input for the plls is generated outside the SoC. It is
+expected that is are defined using standard clock bindings with a
+clock-output-names value of "xti".
+
+Example: Clock controller node:
+
+	clocks: clock-controller@4c000000 {
+		compatible = "samsung,s3c2410-clock";
+		reg = <0x4c000000 0x20>;
+		#clock-cells = <1>;
+	};
+
+Example: UART controller node that consumes the clock generated by the clock
+  controller (refer to the standard clock bindings for information about
+  "clocks" and "clock-names" properties):
+
+	serial@50004000 {
+		compatible = "samsung,s3c2440-uart";
+		reg = <0x50004000 0x4000>;
+		interrupts = <1 23 3 4>, <1 23 4 4>;
+		clock-names = "uart", "clk_uart_baud2";
+		clocks = <&clocks PCLK_UART0>, <&clocks PCLK_UART0>;
+		status = "disabled";
+	};