1To understand all the Linux-USB framework, you'll use these resources:
   3    * This source code.  This is necessarily an evolving work, and
   4      includes kerneldoc that should help you get a current overview.
   5      ("make pdfdocs", and then look at "usb.pdf" for host side and
   6      "gadget.pdf" for peripheral side.)  Also, Documentation/usb has
   7      more information.
   9    * The USB 2.0 specification (from, with supplements
  10      such as those for USB OTG and the various device classes.
  11      The USB specification has a good overview chapter, and USB
  12      peripherals conform to the widely known "Chapter 9".
  14    * Chip specifications for USB controllers.  Examples include
  15      host controllers (on PCs, servers, and more); peripheral
  16      controllers (in devices with Linux firmware, like printers or
  17      cell phones); and hard-wired peripherals like Ethernet adapters.
  19    * Specifications for other protocols implemented by USB peripheral
  20      functions.  Some are vendor-specific; others are vendor-neutral
  21      but just standardized outside of the team.
  23Here is a list of what each subdirectory here is, and what is contained in
  26core/           - This is for the core USB host code, including the
  27                  usbfs files and the hub class driver ("khubd").
  29host/           - This is for USB host controller drivers.  This
  30                  includes UHCI, OHCI, EHCI, and others that might
  31                  be used with more specialized "embedded" systems.
  33gadget/         - This is for USB peripheral controller drivers and
  34                  the various gadget drivers which talk to them.
  37Individual USB driver directories.  A new driver should be added to the
  38first subdirectory in the list below that it fits into.
  40image/          - This is for still image drivers, like scanners or
  41                  digital cameras.
  42../input/       - This is for any driver that uses the input subsystem,
  43                  like keyboard, mice, touchscreens, tablets, etc.
  44../media/       - This is for multimedia drivers, like video cameras,
  45                  radios, and any other drivers that talk to the v4l
  46                  subsystem.
  47../net/         - This is for network drivers.
  48serial/         - This is for USB to serial drivers.
  49storage/        - This is for USB mass-storage drivers.
  50class/          - This is for all USB device drivers that do not fit
  51                  into any of the above categories, and work for a range
  52                  of USB Class specified devices. 
  53misc/           - This is for all USB device drivers that do not fit
  54                  into any of the above categories.
  55 kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.