Sometimes, you've got a serial card that isn't included in the kernel's list of known devices for some reason. It could be that it is just a very small manufacturer, or perhaps the card you've got is newer than the kernel you've got. In either case, as long as the card you have is a 16550 UART, you should be fine. This little gem will get your card recognized and working smoothly. First, you've got to see if your card is even seen by the kernel. You can do this with

lspci

If the kernel lists it as an 'Unknown' device, then it won't show up in