dt: document the of_serial bindings

The of_serial bindings can be used to register a number of serial
devices.  Document this binding with all of the others.

v3: remove device-type and clarify used-by-rtas

Signed-off-by: Jamie Iles <jamie@jamieiles.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

diff --git a/Documentation/devicetree/bindings/tty/serial/of-serial.txt b/Documentation/devicetree/bindings/tty/serial/of-serial.txt
new file mode 100644 (file)
index 0000000..35e53ae
--- /dev/null
+++ b/Documentation/devicetree/bindings/tty/serial/of-serial.txt
@@ -0,0 +1,33 @@
+* UART (Universal Asynchronous Receiver/Transmitter)
+
+Required properties:
+- compatible : one of:
+       - "ns8250"
+       - "ns16450"
+       - "ns16550a"
+       - "ns16550"
+       - "ns16750"
+       - "ns16850"
+       - "nvidia,tegra250-uart"
+       - "ibm,qpace-nwp-serial"
+       - "serial" if the port type is unknown.
+- reg : offset and length of the register set for the device.
+- interrupts : should contain uart interrupt.
+- clock-frequency : the input clock frequency for the UART.
+
+Optional properties:
+- current-speed : the current active speed of the UART.
+- reg-offset : offset to apply to the mapbase from the start of the registers.
+- reg-shift : quantity to shift the register offsets by.
+- used-by-rtas : set to indicate that the port is in use by the OpenFirmware
+  RTAS and should not be registered.
+
+Example:
+
+       uart@80230000 {
+               compatible = "ns8250";
+               reg = <0x80230000 0x100>;
+               clock-frequency = <3686400>;
+               interrupts = <10>;
+               reg-shift = <2>;
+       };