dt-bindings: usb: Introduce GPIO-based SBU mux

Introduce a binding for GPIO-based mux hardware used for connecting,
disconnecting and switching orientation of the SBU lines in USB Type-C
applications.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

Documentation/devicetree/bindings/usb/gpio-sbu-mux.yaml

+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: "http://devicetree.org/schemas/usb/gpio-sbu-mux.yaml#"
+$schema: "http://devicetree.org/meta-schemas/core.yaml#"
+
+title: GPIO-based SBU mux
+
+maintainers:
+  - Bjorn Andersson <bjorn.andersson@linaro.org>
+
+description:
+  In USB Type-C applications the SBU lines needs to be connected, disconnected
+  and swapped depending on the altmode and orientation. This binding describes
+  a family of hardware which perform this based on GPIO controls.
+
+properties:
+  compatible:
+    items:
+      - enum:
+          - onnn,fsusb43l10x
+          - pericom,pi3usb102
+      - const: gpio-sbu-mux
+
+  enable-gpios:
+    description: Switch enable GPIO
+
+  select-gpios:
+    description: Orientation select
+
+  vcc-supply:
+    description: power supply
+
+  mode-switch:
+    description: Flag the port as possible handle of altmode switching
+    type: boolean
+
+  orientation-switch:
+    description: Flag the port as possible handler of orientation switching
+    type: boolean
+
+  port:
+    $ref: /schemas/graph.yaml#/properties/port
+    description:
+      A port node to link the SBU mux to a TypeC controller for the purpose of
+      handling altmode muxing and orientation switching.
+
+required:
+  - compatible
+  - enable-gpios
+  - select-gpios
+  - mode-switch
+  - orientation-switch
+  - port
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+
+    sbu-mux {
+      compatible = "pericom,pi3usb102", "gpio-sbu-mux";
+
+      enable-gpios = <&tlmm 101 GPIO_ACTIVE_LOW>;
+      select-gpios = <&tlmm 164 GPIO_ACTIVE_HIGH>;
+
+      mode-switch;
+      orientation-switch;
+
+      port {
+        endpoint {
+          remote-endpoint = <&pmic_glink_dp0_sbu>;
+        };
+      };
+    };
+...