driver-api/usb/usb.rst

11 workstation, to a number of peripheral devices. USB uses a tree
14 support several such trees of USB devices, usually
31 Linux can run inside USB devices as well as on the hosts that control
32 the devices. But USB device drivers running inside those peripherals
40 Host-side drivers for USB devices talk to the "usbcore" APIs. There are
44 of USB devices) and several different kinds of *host controller
68    USB device drivers actually bind to interfaces, not devices. Think of
69    them as "interface drivers", though you may not see many devices
70    where the distinction is important. *Most USB devices are simple,
115 devices and debugfs interfaces. That file is itself included by
133 drivers and devices, and support passing buffers through usbcore to some
220 character devices through some programming library that wraps it.
246    making device requests, including I/O to devices. (Purely for access
252 always leave the devices plugged in to the same hub port. *Don't even
255 them. HID and networking devices expose these stable IDs, so that for
287 you can't rely on them for stable access to devices.  For example,
288 it's relatively common for devices to re-enumerate while they are
301 in text form by the ``/sys/kernel/debug/usb/devices`` file, described later.
304 devices.  You would open the ``/dev/bus/usb/BBB/DDD`` file read/write,
311 for how to access devices through those files.
326 and ignores most devices. In either case, it should :c:func:`read()`
338 requests; some devices don't need more complex interactions than those.
346 *interrupt* transfers work with low speed devices. Both interrupt and
382 affecting things like which endpoints are available. Many devices only
473     devices what device special file should be used. Two pre-defined
476     devices.
690 The USB devices
693 The USB devices are now exported via debugfs:
695 -  ``/sys/kernel/debug/usb/devices`` ... a text file showing each of the USB
696    devices on known to the kernel, and their configuration descriptors.
697    You can also poll() this to learn about new devices.
699 /sys/kernel/debug/usb/devices
708 to detect when devices are added or removed::
713     fd = open("/sys/kernel/debug/usb/devices", O_RDONLY);
749 /sys/kernel/debug/usb/devices output format  argument
768 	|   |      |      |       |       |__Count of devices at this level
878 USB devices may have multiple configurations, each of which act
881 one device configuration can be active at a time; most devices
912 only one driver may bind to an interface at a time.  Most devices
945 example, use something like ``grep ^T: /sys/kernel/debug/usb/devices``  argument
947 ``grep -i ^[tdp]: /sys/kernel/debug/usb/devices`` can be used to list
954 ``/sys/kernel/debug/usb/devices``.)
957 of the USB devices on a system's root hub.  (See more below
964 (in milliamps) that a system's USB devices are using.
965 For example, ``grep ^C: /sys/kernel/debug/usb/devices``.