Document: devicetree: add OF documents for lantiq falcon pinctrl

Lantiq FALCON pinmux controller

Required properties:

- compatible: "lantiq,pinctrl-falcon"

- reg: Should contain the physical address and length of the gpio/pinmux

  register range

Please refer to pinctrl-bindings.txt in this directory for details of the

common pinctrl bindings used by client devices, including the meaning of the

phrase "pin configuration node".

Lantiq's pin configuration nodes act as a container for an abitrary number of

subnodes. Each of these subnodes represents some desired configuration for a

pin, a group, or a list of pins or groups. This configuration can include the

mux function to select on those group(s), and two pin configuration parameters:

pull-up and open-drain

The name of each subnode is not important as long as it is unique; all subnodes

should be enumerated and processed purely based on their content.

Each subnode only affects those parameters that are explicitly listed. In

other words, a subnode that lists a mux function but no pin configuration

parameters implies no information about any pin configuration parameters.

Similarly, a pin subnode that describes a pullup parameter implies no

information about e.g. the mux function.

We support 2 types of nodes.

Definition of mux function groups:

Required subnode-properties:

- lantiq,groups : An array of strings. Each string contains the name of a group.

  Valid values for these names are listed below.

- lantiq,function: A string containing the name of the function to mux to the

  group. Valid values for function names are listed below.

Valid values for group and function names:

  mux groups:

    por, ntr, ntr8k, hrst, mdio, bootled, asc0, spi, spi cs0, spi cs1, i2c,

    jtag, slic, pcm, asc1

  functions:

    rst, ntr, mdio, led, asc, spi, i2c, jtag, slic, pcm

Definition of pin configurations:

Required subnode-properties:

- lantiq,pins : An array of strings. Each string contains the name of a pin.

  Valid values for these names are listed below.

Optional subnode-properties:

- lantiq,pull: Integer, representing the pull-down/up to apply to the pin.

    0: none, 1: down

- lantiq,drive-current: Boolean, enables drive-current

- lantiq,slew-rate: Boolean, enables slew-rate

Example:

	pinmux0 {

		compatible = "lantiq,pinctrl-falcon";

		pinctrl-names = "default";

		pinctrl-0 = <&state_default>;

		state_default: pinmux {

			asc0 {

				lantiq,groups = "asc0";

				lantiq,function = "asc";

			};

			ntr {

				lantiq,groups = "ntr8k";

				lantiq,function = "ntr";

			};

			i2c {

				lantiq,groups = "i2c";

				lantiq,function = "i2c";

			};

			hrst {

				lantiq,groups = "hrst";

				lantiq,function = "rst";

			};

		};

	};