Say Y here if you want to build support for the IrTTY line
discipline. To compile it as a module, choose M here: the module
will be called irtty-sir. IrTTY makes it possible to use Linux's
own serial driver for all IrDA ports that are 16550 compatible.
Most IrDA chips are 16550 compatible so you should probably say Y
to this option. Using IrTTY will however limit the speed of the
connection to 115200 bps (IrDA SIR mode).

If unsure, say Y.