Upping baud rate for ttyS0

I've downloaded the source RPM for the 3.10 kernel. I'm looking for the driver code that I need to modify to support higher baud rates than that permitted by the current serial driver (B115200 when using stty or cfsetispeed() + tcsetattr()). I've looked in the drivers/tty/serial/ source files but am uncertain where to begin. Any pointer would be appreciated. ---John