Document: devicetree: add OF documents for lantiq falcon pinctrl

Signed-off-by: John Crispin <blogic@openwrt.org>
Signed-off-by: Thomas Langer <thomas.langer@lantiq.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Cc: devicetree-discuss@lists.ozlabs.org
Cc: linux-kernel@vger.kernel.org

Documentation/devicetree/bindings/pinctrl/lantiq,falcon-pinumx.txt

+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";
+			};
+		};
+	};