of: Add NVIDIA Tegra XUSB pad controller binding

This patch adds the device tree binding documentation for the XUSB pad
controller found on NVIDIA Tegra SoCs. It exposes both pinmuxing and PHY
capabilities.
Tested-by: Mikko Perttunen <mperttunen@nvidia.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>

Documentation/devicetree/bindings/pinctrl/nvidia,tegra124-xusb-padctl.txt

+Device tree binding for NVIDIA Tegra XUSB pad controller
+========================================================
+
+The Tegra XUSB pad controller manages a set of lanes, each of which can be
+assigned to one out of a set of different pads. Some of these pads have an
+associated PHY that must be powered up before the pad can be used.
+
+This document defines the device-specific binding for the XUSB pad controller.
+
+Refer to pinctrl-bindings.txt in this directory for generic information about
+pin controller device tree bindings and ../phy/phy-bindings.txt for details on
+how to describe and reference PHYs in device trees.
+
+Required properties:
+--------------------
+- compatible: should be "nvidia,tegra124-xusb-padctl"
+- reg: Physical base address and length of the controller's registers.
+- resets: Must contain an entry for each entry in reset-names.
+  See ../reset/reset.txt for details.
+- reset-names: Must include the following entries:
+  - padctl
+- #phy-cells: Should be 1. The specifier is the index of the PHY to reference.
+  See <dt-bindings/pinctrl/pinctrl-tegra-xusb.h> for the list of valid values.
+
+Lane muxing:
+------------
+
+Child nodes contain the pinmux configurations following the conventions from
+the pinctrl-bindings.txt document. Typically a single, static configuration is
+given and applied at boot time.
+
+Each subnode describes groups of lanes along with parameters and pads that
+they should be assigned to. The name of these subnodes is not important. All
+subnodes should be parsed solely based on their content.
+
+Each subnode only applies the parameters that are explicitly listed. In other
+words, if a subnode that lists a function but no pin configuration parameters
+implies no information about any pin configuration parameters. Similarly, a
+subnode that describes only an IDDQ parameter implies no information about
+what function the pins are assigned to. For this reason even seemingly boolean
+values are actually tristates in this binding: unspecified, off or on.
+Unspecified is represented as an absent property, and off/on are represented
+as integer values 0 and 1.
+
+Required properties:
+- nvidia,lanes: An array of strings. Each string is the name of a lane.
+
+Optional properties:
+- nvidia,function: A string that is the name of the function (pad) that the
+  pin or group should be assigned to. Valid values for function names are
+  listed below.
+- nvidia,iddq: Enables IDDQ mode of the lane. (0: no, 1: yes)
+
+Note that not all of these properties are valid for all lanes. Lanes can be
+divided into three groups:
+
+  - otg-0, otg-1, otg-2:
+
+    Valid functions for this group are: "snps", "xusb", "uart", "rsvd".
+
+    The nvidia,iddq property does not apply to this group.
+
+  - ulpi-0, hsic-0, hsic-1:
+
+    Valid functions for this group are: "snps", "xusb".
+
+    The nvidia,iddq property does not apply to this group.
+
+  - pcie-0, pcie-1, pcie-2, pcie-3, pcie-4, sata-0:
+
+    Valid functions for this group are: "pcie", "usb3", "sata", "rsvd".
+
+
+Example:
+========
+
+SoC file extract:
+-----------------
+
+	padctl@0,7009f000 {
+		compatible = "nvidia,tegra124-xusb-padctl";
+		reg = <0x0 0x7009f000 0x0 0x1000>;
+		resets = <&tegra_car 142>;
+		reset-names = "padctl";
+
+		#phy-cells = <1>;
+	};
+
+Board file extract:
+-------------------
+
+	pcie-controller@0,01003000 {
+		...
+
+		phys = <&padctl 0>;
+		phy-names = "pcie";
+
+		...
+	};
+
+	...
+
+	padctl: padctl@0,7009f000 {
+		pinctrl-0 = <&padctl_default>;
+		pinctrl-names = "default";
+
+		padctl_default: pinmux {
+			usb3 {
+				nvidia,lanes = "pcie-0", "pcie-1";
+				nvidia,function = "usb3";
+				nvidia,iddq = <0>;
+			};
+
+			pcie {
+				nvidia,lanes = "pcie-2", "pcie-3",
+					       "pcie-4";
+				nvidia,function = "pcie";
+				nvidia,iddq = <0>;
+			};
+
+			sata {
+				nvidia,lanes = "sata-0";
+				nvidia,function = "sata";
+				nvidia,iddq = <0>;
+			};
+		};
+	};

include/dt-bindings/pinctrl/pinctrl-tegra-xusb.h

+#ifndef _DT_BINDINGS_PINCTRL_TEGRA_XUSB_H
+#define _DT_BINDINGS_PINCTRL_TEGRA_XUSB_H 1
+
+#define TEGRA_XUSB_PADCTL_PCIE 0
+#define TEGRA_XUSB_PADCTL_SATA 1
+
+#endif /* _DT_BINDINGS_PINCTRL_TEGRA_XUSB_H */