pinctrl: zynq: Document DT binding

	Binding for Xilinx Zynq Pinctrl

Required properties:

- compatible: "xlnx,zynq-pinctrl"

- syscon: phandle to SLCR

- reg: Offset and length of pinctrl space in SLCR

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".

Zynq's pin configuration nodes act as a container for an arbitrary 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 pin(s)/group(s), and various pin configuration

parameters, such as pull-up, slew rate, etc.

Each configuration node can consist of multiple nodes describing the pinmux and

pinconf options. Those nodes can be pinmux nodes or pinconf nodes.

The name of each subnode is not important; all subnodes should be enumerated

and processed purely based on their content.

Required properties for pinmux nodes are:

 - groups: A list of pinmux groups.

 - function: The name of a pinmux function to activate for the specified set

   of groups.

Required properties for configuration nodes:

One of:

 - pins: a list of pin names

 - groups: A list of pinmux groups.

The following generic properties as defined in pinctrl-bindings.txt are valid

to specify in a pinmux subnode:

 groups, function

The following generic properties as defined in pinctrl-bindings.txt are valid

to specify in a pinconf subnode:

 groups, pins, bias-disable, bias-high-impedance, bias-pull-up, slew-rate,

 low-power-disable, low-power-enable

 Valid arguments for 'slew-rate' are '0' and '1' to select between slow and fast

 respectively.

 Valid values for groups are:

   ethernet0_0_grp, ethernet1_0_grp, mdio0_0_grp, mdio1_0_grp,

   qspi0_0_grp, qspi1_0_grp, qspi_fbclk, qspi_cs1_grp, spi0_0_grp,

   spi0_1_grp - spi0_2_grp, spi1_0_grp - spi1_3_grp, sdio0_0_grp - sdio0_2_grp,

   sdio1_0_grp - sdio1_3_grp, sdio0_emio_wp, sdio0_emio_cd, sdio1_emio_wp,

   sdio1_emio_cd, smc0_nor, smc0_nor_cs1_grp, smc0_nor_addr25_grp, smc0_nand,

   can0_0_grp - can0_10_grp, can1_0_grp - can1_11_grp, uart0_0_grp - uart0_10_grp,

   uart1_0_grp - uart1_11_grp, i2c0_0_grp - i2c0_10_grp, i2c1_0_grp - i2c1_10_grp,

   ttc0_0_grp - ttc0_2_grp, ttc1_0_grp - ttc1_2_grp, swdt0_0_grp - swdt0_4_grp,

   gpio0_0_grp - gpio0_53_grp, usb0_0_grp, usb1_0_grp

 Valid values for pins are:

   MIO0 - MIO53

 Valid values for function are:

   ethernet0, ethernet1, mdio0, mdio1, qspi0, qspi1, qspi_fbclk, qspi_cs1,

   spi0, spi1, sdio0, sdio0_pc, sdio0_cd, sdio0_wp,

   sdio1, sdio1_pc, sdio1_cd, sdio1_wp,

   smc0_nor, smc0_nor_cs1, smc0_nor_addr25, smc0_nand, can0, can1, uart0, uart1,

   i2c0, i2c1, ttc0, ttc1, swdt0, gpio0, usb0, usb1

The following driver-specific properties as defined here are valid to specify in

a pin configuration subnode:

 - io-standard: Configure the pin to use the selected IO standard according to

   this mapping:

    1: LVCMOS18

    2: LVCMOS25

    3: LVCMOS33

    4: HSTL

Example:

	pinctrl0: pinctrl@700 {

		compatible = "xlnx,pinctrl-zynq";

		reg = <0x700 0x200>;

		syscon = <&slcr>;

		pinctrl_uart1_default: uart1-default {

			mux {

				groups = "uart1_10_grp";

				function = "uart1";

			};

			conf {

				groups = "uart1_10_grp";

				slew-rate = <0>;

				io-standard = <1>;

			};

			conf-rx {

				pins = "MIO49";

				bias-high-impedance;

			};

			conf-tx {

				pins = "MIO48";

				bias-disable;

			};

		};

	};