Add your new source file to the appropriate source directory.
Example: drivers/usb/serial/navman.c
Single file drivers in the common case, even if the file is several thousand lines of code. Only really big drivers are split in several files or have their own directory.
Describe the configuration interface for your new driver
by adding the following lines to the Kconfig file in this directory:
config USB_SERIAL_NAVMAN
tristate "USB Navman GPS device"
depends on USB_SERIAL
help
To compile this driver as a module, choose M here: the
module will be called navman.