linux/Documentation/devicetree/bindings/gpio/gpio_atmel.txt
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   1* Atmel GPIO controller (PIO)
   2
   3Required properties:
   4- compatible: "atmel,<chip>-gpio", where <chip> is at91rm9200 or at91sam9x5.
   5- reg: Should contain GPIO controller registers location and length
   6- interrupts: Should be the port interrupt shared by all the pins.
   7- #gpio-cells: Should be two.  The first cell is the pin number and
   8  the second cell is used to specify optional parameters (currently
   9  unused).
  10- gpio-controller: Marks the device node as a GPIO controller.
  11
  12optional properties:
  13- #gpio-lines: Number of gpio if absent 32.
  14
  15
  16Example:
  17        pioA: gpio@fffff200 {
  18                compatible = "atmel,at91rm9200-gpio";
  19                reg = <0xfffff200 0x100>;
  20                interrupts = <2 4>;
  21                #gpio-cells = <2>;
  22                gpio-controller;
  23                #gpio-lines = <19>;
  24        };
  25
  26