How are people using those ISA cards today? The version of setserial
that I found is not able to set MMIO mode on those. I suppose you

Various ugly hacks, if its tricky we can drop support and see who screams

are not talking about isapnp cards, right? Those should not need to
be handled through the ISA driver at all.

ISAPnP will do it automatically so the ISAPnP case isn't a problem. I've
never sen an ISAPnP port that was anything but standard.