Would anything be gained from having a #ifdef that makes the driver
understand 16550A only ?
A little. Most of the gains can be obtained by just attaching a UART-
specific interrupt handler. My version has the configuration of the
interrupt handler moved out of the config file so that the driver can
configure it better. I only use this to avoid going through siointr()
to siointr1() in the non-COM_MULTIPORT case so far.