This is now the third time I've bought some PCI serial multi-port card (6 to 8 ports) that claimed to have 'Linux support'. If you then read the document, the vendor bluntly tells you that Linux generally doesn't support more than four ports, so if you have two built-in ports, you can only use two more. I've never read such bullshit anywhere else ;)
So after some minor twiddling, I now submitted a patch adding support for this particular 6port device. Apparently there is either a wide variety of such boards, or almost no Linux users... A couple of years ago I added support for an AFAVLAB 8port serial card, to the Linux serial driver.
I think I now know way too much about the serial driver. Not stopping with those two PCI 8250 based boards, I did lots of serial driver hacking for the XServe G5 and also for my recent ARM embedded work. Let's hope I can again advance to some more exciting work in the future.