doc: usb: add initial USB/IP documentation

Add initial USB/IP documentation for the new USB support.

Signed-off-by: Johann Fischer <johann.fischer@nordicsemi.no>

Author: jfischer-no

doc/connectivity/usb/host/usbip.rst

@@ -0,0 +1,79 @@
+.. _usbip:
+
+USB/IP protocol support
+#######################
+
+Overview
+********
+
+New USB support includes initial support for the USB/IP protocol. It is still
+under development and is currently limited to supporting only one device
+connected to the host controller being exported.
+
+USB/IP uses TCP/IP. Both of the underlying connectivity stacks, USB and
+networking, require significant memory resources, which must be considered when
+choosing a platform.
+
+In the USB/IP protocol, a server exports the USB devices and a client imports
+them. USB/IP support in the Zephyr RTOS implements server functionality and
+exports a device connected to a host controller on a device running the Zephyr
+RTOS. A client, typically running the Linux kernel, imports this device. The
+USB/IP protocol is described in `USB/IP protocol documentation`_.
+
+To use USB/IP support, make sure the required modules are loaded on the client side.
+
+.. code-block:: console
+
+   modprobe vhci_hcd
+   modprobe usbip-core
+   modprobe usbip-host
+
+On the client side, you will also need the **usbip** user tool. It can be installed
+using your Linux distribution's package management system or built from Linux
+kernel sources.
+
+There are a few basic commands for everyday use. To list exported USB devices,
+run the following command:
+
+.. code-block:: console
+
+   $ usbip list -r 192.0.2.1
+   Exportable USB devices
+   ======================
+    - 192.0.2.1
+           1-1: NordicSemiconductor : unknown product (2fe3:0001)
+              : /sys/bus/usb/devices/usb1/1-1
+              : Miscellaneous Device / ? / Interface Association (ef/02/01)
+              :  0 - Communications / Abstract (modem) / None (02/02/00)
+              :  1 - CDC Data / Unused / unknown protocol (0a/00/00)
+
+To attach an exported device with busid 1-1:
+
+.. code-block:: console
+
+   $ sudo usbip attach -r 192.0.2.1 -b 1-1
+
+To detach an exported device on port 0:
+
+.. code-block:: console
+
+   $ sudo usbip detach -p 0
+
+USB/IP with native_sim
+**********************
+
+The preferred method to develop with USB/IP support enabled is to use
+:ref:`native_sim <native_sim>`. Use on real hardware is not really tested yet.
+USB/IP requires a network connection, see :ref:`networking_with_native_sim`
+for how to set up the interface on the client side.
+
+Building and running a sample with USB/IP requires extensive configuration,
+you can use usbip-native-sim snippet to configure host and USB/IP support.
+
+.. zephyr-app-commands::
+   :zephyr-app: samples/subsys/usb/cdc_acm
+   :board: native_sim/native/64
+   :gen-args: -DSNIPPET=usbip-native-sim -DEXTRA_DTC_OVERLAY_FILE=app.overlay
+   :goals: build
+
+.. _USB/IP protocol documentation: https://www.kernel.org/doc/html/latest/usb/usbip_protocol.html

doc/connectivity/usb/index.rst

@@ -19,6 +19,7 @@ USB
    device_next/usb_device.rst
    device_next/api/index.rst
    host/api/index.rst
+   host/usbip.rst
 
 **USB Power Delivery support**