The FunctionFS gadget may provide the source/sink interface
not as the first interface (with id == 0) but some different
interface hence a code to find the interface number is
required.

(Note that you will still configure the gadget to report
idProduct == 0xa4a4 (an "echo 0xa4a4
>/sys/module/g_ffs/parameters/usb_product" should suffice) or
configure host to handle 0x0525:0xa4ac devices using the
usbtest driver.)
Signed-off-by: NMichal Nazarewicz <m.nazarewicz@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

The testusb program just issues ioctls to perform the tests
implemented by the kernel driver.  It can generate a variety
of transfer patterns; you should make sure to test both regular
streaming and mixes of  transfer sizes (including short transfers).

For more information on how this can be used and on USB testing
refer to <URL:http://www.linux-usb.org/usbtest/>.
Signed-off-by: NMichal Nazarewicz <m.nazarewicz@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>