The Serial gadget driver, which implements a virtual COM port (like RS232) over USB, is provided with the Linux 2.6 kernel sources.
In order to use the Serial gadget driver with the NET 2272, you will need the controller driver for the NET 2272. PLX provides the NET 2272 controller driver for Linux 2.6.
File: RE061204-net2272-linux2.6.11.tgz
Description: NET 2272 controller driver for Linux 2.6.11
File: RE061204-net2272-linux2.6.18.tgz
Description: NET 2272 controller driver for Linux 2.6.18