Is it possible to access the serial port module from another kernel module?

Im supposed to write a driver for a hitech pws touchpad which communicates through the serial port. I dont want the touchpad driver built into the user space program, i want it as a kernel module so i can access the touchpad with open() read() write() etc as a char device. Problem is though that i cant use open() and the other file operations to get hold of /dev/ttys0 from the touchpad kernel driver since these only seem to be able to use from user space programs.

Any suggestions how I can solve this? Or do I need to write my own serial port driver and skip the already functional one?

thanks
/johan