The easy way to fix this is (as root) to edit /etc/default/grub and append ” 8250.nr_uarts=8″ (without quotes) to the end of the line “GRUB_CMDLINE_LINUX_DEFAULT=”
You can set any number up to 32 as the number of serial ports this way.
You then have to run “update-grub” as root. After rebooting you should have the serial ports working.