linux/Documentation/devicetree/bindings/tty/serial/of-serial.txt
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   1* UART (Universal Asynchronous Receiver/Transmitter)
   2
   3Required properties:
   4- compatible : one of:
   5        - "ns8250"
   6        - "ns16450"
   7        - "ns16550a"
   8        - "ns16550"
   9        - "ns16750"
  10        - "ns16850"
  11        - "nvidia,tegra20-uart"
  12        - "nxp,lpc3220-uart"
  13        - "ibm,qpace-nwp-serial"
  14        - "altr,16550-FIFO32"
  15        - "altr,16550-FIFO64"
  16        - "altr,16550-FIFO128"
  17        - "serial" if the port type is unknown.
  18- reg : offset and length of the register set for the device.
  19- interrupts : should contain uart interrupt.
  20- clock-frequency : the input clock frequency for the UART
  21         or
  22  clocks phandle to refer to the clk used as per Documentation/devicetree
  23  /bindings/clock/clock-bindings.txt
  24
  25Optional properties:
  26- current-speed : the current active speed of the UART.
  27- reg-offset : offset to apply to the mapbase from the start of the registers.
  28- reg-shift : quantity to shift the register offsets by.
  29- reg-io-width : the size (in bytes) of the IO accesses that should be
  30  performed on the device.  There are some systems that require 32-bit
  31  accesses to the UART (e.g. TI davinci).
  32- used-by-rtas : set to indicate that the port is in use by the OpenFirmware
  33  RTAS and should not be registered.
  34- no-loopback-test: set to indicate that the port does not implements loopback
  35  test mode
  36- fifo-size: the fifo size of the UART.
  37- auto-flow-control: one way to enable automatic flow control support. The
  38  driver is allowed to detect support for the capability even without this
  39  property.
  40
  41Example:
  42
  43        uart@80230000 {
  44                compatible = "ns8250";
  45                reg = <0x80230000 0x100>;
  46                clock-frequency = <3686400>;
  47                interrupts = <10>;
  48                reg-shift = <2>;
  49        };
  50