The Serial Gadget talks to the Linux-USB generic serial driver.
This driver supports a CDC-ACM module option, which can be used
to interoperate with MS-Windows hosts or with the Linux-USB
"cdc-acm" driver.

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

For more information, see <a href="https://www.kernel.org/doc/Documentation/usb/gadget_serial.txt
which">Documentation/usb/gadget_serial.txt
which</a> includes instructions and a "driver info file" needed to
make MS-Windows work with this driver.

source code:

drivers/usb/gadget/