Quoting Stephen Boyd (2016-09-13 18:42:46)

On the db410c 96boards platform we have a TC7USB40MU[1] on the
board to mux the D+/D- lines from the SoC between a micro usb
"device" port and a USB hub for "host" roles. Upon a role switch,
we need to change this mux to forward the D+/D- lines to either
the port or the hub. Therefore, introduce a driver for this
device that intercepts extcon USB_HOST events and logically
asserts a gpio to mux the "host" D+/D- lines when a host cable is
attached. When the cable goes away, it will logically deassert
the gpio and mux the "device" lines.

[1] https://toshiba.semicon-storage.com/ap-en/product/logic/bus-switch/detail.TC7USB40MU.html

Cc: MyungJoo Ham <myungjoo.ham@samsung.com>
Cc: Chanwoo Choi <cw00.choi@samsung.com>
Cc: <redacted>
Signed-off-by: Stephen Boyd <redacted>
---

Should I make the extcon part optional? I could see a case where there are two
"OTG" ports connected to the mux (or two hubs), and for some reason the
software may want to mux between them at runtime. If we mandate an extcon,
that won't be possible to support. Perhaps it would be better to have
the node, but connect it to the usb controller with a phandle (maybe of_graph
endpoints would be useful too) so that when the controller wants to mux over
a port it can do so.

Here's some dts mock-up on top of the db410c for the of_graph stuff. I
haven't written any code around it, but the idea is to allow the binding
to specify how the mux is connected to upstream and downstream D+/D-
lines. This way, we can do some dt parsing of the endpoints and their
parent nodes to figure out if the mux needs to be set high or low to use
a device connector or a usb hub based on if the id cable is present.
Maybe I'm over thinking things though and we could just have a DT
property for that.

	soc {
		usb at 78d9000 {
			extcon = <&usb_id>, <&usb_id>;
			usb-controller; // needed?

			ports {
				#address-cells = <1>;
				#size-cells = <0>;

				port at 0 {
					#address-cells = <1>;
					#size-cells = <0>;
					reg = <0>;

					usb_output: endpoint at 0 { // USB D+/D-
						reg = <0>;
						remote-endpoint = <&usb_switch_input>;
					};
				};
			};
		};
	};

	usb2513 {
		compatible = "smsc,usb3503";
		reset-gpios = <&pm8916_gpios 3 GPIO_ACTIVE_LOW>;
		initial-mode = <1>;
		usb-hub; // indicate this is a hub

		ports {
			#address-cells = <1>;
			#size-cells = <0>;

			port at 0 {
				#address-cells = <1>;
				#size-cells = <0>;
				reg = <0>;

				usb_hub_input: endpoint at 0 { // USB{DP,DM}_UP
					reg = <0>;
					remote-endpoint = <&usb_switch_hub_ep>;
				};

				usb_hub_output1: endpoint at 1 { // USB{DP,DM}_DN1
					reg = <1>;
					remote-endpoint = <&usb_a2_connector>;
				};

				usb_hub_output2: endpoint at 2 { // USB{DP,DM}_DN2
					reg = <2>;
					remote-endpoint = <&usb_a1_connector>;
				};

				usb_hub_output3: endpoint at 3 { // USB{DP,DM}_DN3
					reg = <3>;
					// goes to expansion connector
				};
			};
		};
	};

	usb_id: usb-id {
		compatible = "linux,extcon-usb-gpio";
		id-gpio = <&msmgpio 121 GPIO_ACTIVE_HIGH>;
		pinctrl-names = "default";
		pinctrl-0 = <&usb_id_default>;
	};

	usb-switch {
		compatible = "toshiba,tc7usb40mu";
		switch-gpios = <&pm8916_gpios 4 GPIO_ACTIVE_HIGH>;
		extcon = <&usb_id>;
		pinctrl-names = "default";
		pinctrl-0 = <&usb_sw_sel_pm>;

		ports {
			#address-cells = <1>;
			#size-cells = <0>;

			port at 0 {
				#address-cells = <1>;
				#size-cells = <0>;
				reg = <0>;

				usb_switch_input: endpoint at 0 { // D+/D-
					reg = <0>;
					remote-endpoint = <&usb_output>;
				};

				usb_switch_device_ep: endpoint at 1 { // D1+/D1-
					reg = <1>;
					remote-endpoint = <&usb_ub_connector>;
				};

				usb_switch_hub_ep: endpoint at 2 { // D2+/D2-
					reg = <2>;
					remote-endpoint = <&usb_hub_input>;
				};
			};
		};
	};

	uB-connector {
		compatible = "usb-ub-connector";
		#address-cells = <1>;
		#size-cells = <0>;
		usb-connector;
		port at 0 {
			#address-cells = <1>;
			#size-cells = <0>;
			reg = <0>;
			usb_ub_connector: endpoint at 0 {
				reg = <0>;
				remote-endpoint = <&usb_switch_device_ep>;
			};
		};
	};

	usb-A-connector1 {
		compatible = "usb-A-connector";
		#address-cells = <1>;
		#size-cells = <0>;
		usb-connector;
		port at 0 {
			#address-cells = <1>;
			#size-cells = <0>;
			reg = <0>;
			usb_a1_connector: endpoint at 0 {
				reg = <0>;
				remote-endpoint = <&usb_hub_output2>;
			};
		};
	};

	usb-A-connector2 {
		compatible = "usb-A-connector";
		#address-cells = <1>;
		#size-cells = <0>;
		usb-connector;
		port at 0 {
			#address-cells = <1>;
			#size-cells = <0>;
			reg = <0>;
			usb_a2_connector: endpoint at 0 {
				reg = <0>;
				remote-endpoint = <&usb_hub_output1>;
			};
		};
	};
};