[PATCH 2/3] meson_uart: add documentation for the dt-bindings of meson_uart

[Helmut Klein]

this patch adds the dt-bindings information for meson_uart.

i'm pretty sure, that this is NOT the final version.

diff -Napur a/Documentation/devicetree/bindings/serial/meson_uart.txt 
b/Documentation/devicetree/bindings/serial/meson_uart.txt
--- a/Documentation/devicetree/bindings/serial/meson_uart.txt	1970-01-01 
01:00:00.000000000 +0100
+++ b/Documentation/devicetree/bindings/serial/meson_uart.txt	2017-03-22 
20:05:06.461911566 +0100
@@ -0,0 +1,42 @@
+* Amlogic Meson UART, used in multiple SoCs (e.g. S905, s905X, ...)
+
+Required properties:
+- compatible		: "amlogic,meson-uart"
+- reg			: offset and length of the register set for the device.
+- pinctrl		: i/o pins to use for the uart function (pin mux)
+- interrupts		: device interrupt
+- clocks		: the baud rate clock for the UART and optional the core clock
+
+e.g.
+uart_AO: serial at 4c0 {
+	compatible = "amlogic,meson-uart";
+	reg = <0x0 0x004c0 0x0 0x14>;
+	pinctrl-0 = <&uart_ao_a_pins>;
+	interrupts = <GIC_SPI 193 IRQ_TYPE_EDGE_RISING>;
+	clocks = <&xtal>;
+	status = "ok";
+};
+
+Optional properties:
+- clock-names		: the names of the clocks: "xtal" and optional "core"
+- pinctrl-names		: the names of the pin controls, must be "default"
+
+e.g.
+uart_A: serial at 84c0 {
+	compatible = "amlogic,meson-uart";
+	reg = <0x0 0x84c0 0x0 0x14>;
+	pinctrl-0 = <&uart_a_pins &uart_a_cts_rts_pins>;
+	pinctrl-names = "default";
+	interrupts = <GIC_SPI 26 IRQ_TYPE_EDGE_RISING>;
+	clocks = <&xtal>, <&clkc CLKID_UART0>;
+	clock-names = "xtal", "core";
+	status = "ok";
+};
+
+Note: Each port should have an alias correctly numbered in "aliases" node.
+
+e.g.
+aliases {
+	serial0 = &uart_AO;
+	serial1 = &uart_A;
+};