Linux – setserial: Cannot get serial info: Inappropriate ioctl for device

A couple of things strike me about what I see in your /proc and dmesg output:

• You shouldn't try to share an IRQ between devices. It may work, but the intention with ISA is that each device on the bus that needs an interrupt line to work gets its own IRQ. If your serial port cards don't give you enough IRQ options, you may simply not be able to use them all together in that PC.

• The I/O addresses you are using for the second pair of serial ports are nonstandard. ttyS2 is normally at 0x3E8 and ttyS3 is normally at 0x2E8. I would move those if you have that option with the serial card. (There are no standard I/O addresses or IRQs for ttyS4 and up.)

Aside from all that, if I needed 6 serial ports on a Linux box, I wouldn't try to use plain old serial port adapter cards. I would use something like a Digi AccelePort. They still offer one that will work in your ISA slots, the Xe model. If you need cheap, you should be able to find one floating around on the used market; they were very popular back in the day.

I think I found the solution to this, in case anyone googles it in the future. My 10.04 did not load usbserial by default, so I had to do it with modprobe usbserial vendor=0x0403 product=0x6001, which I added to /etc/modules. After I upgraded, my 12.04 loads the ftdi_sio driver by default, which is for the embedded device I am using. I didn't change my /etc/modules back, so usbserial was being loaded too, and probably causing some sort of conflict. I removed usbserial from /etc/modules and rebooted, and it worked.

If I were really confident in this solution I would confirm it by rebooting my machine again and seeing if the serial port came up properly - but I would feel pretty silly if I rebooted and lost the connection, since I do need to get work done while I have it.