Serial port on Open Firmware platform bus

modulename: 8250_of.ko

and/or

of_serial.ko

configname: CONFIG_SERIAL_OF_PLATFORM

Linux Kernel Configuration
└─>Device Drivers
└─>Character devices
└─>Serial drivers
└─>Serial port on Open Firmware platform bus
In linux kernel since version 2.6.21.1 (release Date: 2007-04-27)  
If you have a PowerPC based system that has serial ports
on a platform specific bus, you should enable this option.
Currently, only 8250 compatible ports are supported, but
others can easily be added.

source code:
drivers/tty/serial/of_serial.c