On Wed, Sep 14, 2016 at 01:55:02AM -0700, Stephen Boyd wrote:

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

quoted

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.

I've mentioned my opinion on extcon before. The first clue that it needs 
work is a Linux subsystem name is used for the binding. 

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.

I think the connector nodes are on the right track, but of-graph doesn't 
work here because we already have a way to describe USB buses in DT. 
Following that, would something like this work for you? The vbus-supply 
and id-gpios are just examples and may not always be there like if the 
hub controls each port's vbus directly.

usb-controller@1234 {
	usb-switch@0 {
		compatible = "toshiba,tc7usb40mu";
		hub@0 {
			compatible = "some-hub";
			port@0 {
				compatible = "usb-A-connector"
				vbus-supply = ...;
			};
			port@1 {
				compatible = "usb-A-connector"
				vbus-supply = ...;
			};

		};
		connector@1 {
			compatible = "usb-ub-connector";
			vbus-supply = ...;
			id-gpios = <>;
		};
	};
};

Rob