RFC USB: serial: add device tree (and serdev) support

These are some patches I've been using to test out using serdev with USB serial. Adding device-tree support to USB serial is really a separate matter and could be merged before the remaining issues related to hotplug are addressed for serdev.

Note that this has been a low-intensity on-going effort where most prerequisites are already upstream including USB device tree support (4.15), device-tree node sharing (4.13), musb device-node propagation (linux-next) and various fixes along the way (driver core, usb core, musb).

What left to be decided is how to deal with multi-port devices. This series uses child nodes to represent each port, which may be a little counter-intuitive for devices (or rather interfaces) with just a single port:

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

		serial@0 {
			reg = <0>;
		};
	};

but I still think this it how it needs to be implemented.

Another thing that's currently lacking is binding documentation.

For completeness (and per request), the second patch enables serdev support and can be used for testing purposes. The third patch can be used as a base for testing this on a BBB and describes two USB serial devices attached to an external hub.

Note that this series depends on a couple of patches (for usb-serial and musb) that are still in linux-next. For convenience, I've prepared a branch here:

https://git.kernel.org/pub/scm/linux/kernel/git/johan/usb-serial.git/log/?h=usb-serial-of

Johan

Johan Hovold (3):
USB: serial: add device-tree support
USB: serial: enable serdev support
dbg: ARM: dts: boneblack: add USB topology and serdev nodes

 arch/arm/boot/dts/am335x-boneblack.dts | 57 ++++++++++++++++++++++++++
 drivers/usb/serial/bus.c               |  7 ++--
 drivers/usb/serial/usb-serial.c        | 28 ++++++++++++-
 3 files changed, 88 insertions(+), 4 deletions(-)

2.17.0