Here is a list of what each subdirectory here is, and what is contained in
them.

core/		- This is for the core USB host code, including the
		  usbfs files.

host/		- This is for all of the USB host drivers.  This
		  includes UHCI, OHCI, EHCI, and any others that might
		  be created in the future.

gadget/		- This is for all of the USB device controller drivers. 


Individual USB driver directories.  A new driver should be added to the
first subdirectory in the list below that it fits into.

image/		- This is for still image drivers, like scanners or
		  digital cameras.
input/		- This is for any driver that uses the input subsystem,
		  like keyboard, mice, touchscreens, tablets, etc.
media/		- This is for multimedia drivers, like video cameras,
		  radios, and any other drivers that talk to the v4l
		  subsystem.
net/		- This is for network drivers.
serial/		- This is for USB to serial drivers.
storage/	- This is for USB mass-storage drivers.
class/		- This is for all USB device drivers that do not fit
		  into any of the above categories, and work for a range
		  of USB Class specified devices. 
misc/		- This is for all USB device drivers that do not fit
		  into any of the above categories.