Add documentation for the Atmel PIO4 controller introduced with SAMA5D2
chip family.

Signed-off-by: Ludovic Desroches <redacted>
---
 .../bindings/pinctrl/atmel,at91-pio4-pinctrl.txt   | 90 ++++++++++++++++++++++
 1 file changed, 90 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/pinctrl/atmel,at91-pio4-pinctrl.txt

diff --git a/Documentation/devicetree/bindings/pinctrl/atmel,at91-pio4-pinctrl.txt b/Documentation/devicetree/bindings/pinctrl/atmel,at91-pio4-pinctrl.txt
new file mode 100644
index 0000000..61ac757
--- /dev/null
+++ b/Documentation/devicetree/bindings/pinctrl/atmel,at91-pio4-pinctrl.txt

@@ -0,0 +1,90 @@
+* Atmel PIO4 Controller
+
+The Atmel PIO4 controller is used to select the function of a pin and to
+configure it.
+
+Required properties:
+- compatible: "atmel,sama5d2-pinctrl".
+- reg: base address and length of the PIO controller.
+- interrupts: interrupt outputs from the controller, one for each bank.
+- interrupt-controller: mark the device node as an interrupt controller.
+- #interrupt-cells: should be two.
+- gpio-controller: mark the device node as a gpio controller.
+- #gpio-cells: should be two.
+
+Please refer to ../gpio/gpio.txt and ../interrupt-controller/interrupts.txt for
+a general description of GPIO and interrupt bindings.
+
+Please refer to pinctrl-bindings.txt in this directory for details of the
+common pinctrl bindings used by client devices.
+
+Subnode format
+Each node (or subnode) will list the pins it needs and how to configured these
+pins.
+
+	node {
+		pinmux = <PIN_NUMBER_PINMUX>;
+		GENERIC_PINCONFIG;
+	};
+
+Required properties:
+- pinmux: integer array. Each integer represents a pin number plus mux and
+ioset settings. Use the macros from boot/dts/<soc>-pinfunc.h file to get the
+right representation of the pin.
+
+Optional properties:
+- GENERIC_PINCONFIG: generic pinconfig options to use, bias-disable,
+bias-pull-down, bias-pull-up, drive-open-drain, input-schmitt-enable,
+input-debounce, output-low, output-high.