Gadget Zero is a two-configuration device. It either sinks and
sources bulk data; or it loops back a configurable number of
transfers. It also implements control requests, for "chapter 9"
conformance. The driver needs only two bulk-capable endpoints, so
it can work on top of most device-side usb controllers. It's
useful for testing, and is also a working example showing how
USB "gadget drivers" can be written.

Make this be the first driver you try using on top of any new
USB peripheral controller driver. Then you can use host-side
test software, like the "usbtest" driver, to put your hardware
and its driver through a basic set of functional tests.

Gadget Zero also works with the host-side "usb-skeleton" driver,
and with many kinds of host-side test software. You may need
to tweak product and vendor IDs before host software knows about
this device, and arrange to select an appropriate configuration.

Say "y" to link the driver statically, or "m" to build a
dynamically linked module called "g_zero".

source code:

drivers/usb/gadget/legacy/