5.2 Serial Port Driver Example
For PCI serial ports (and for ISA PnP serial ports after 2.4 kernels) the serial driver detects the type of serial port and PnP configures it. Unfortunately, there may be some PCI serial ports that are not supported yet.
For the standard ISA serial port with very old older versions of the kernel and serial driver (not for multiport cards) the driver probes two standard addresses for serial ports. It doesn't probe for IRQs but it just assigns the "standard" IRQ to the first two serial ports. This could be wrong.
For anything else the configuration file for the setserial program must be manually modified. See Serial-HOWTO for more details. You use setserial to inform the driver of the IO address and Setserial is often run from a start-up file. In newer versions there is a /etc/serial.conf file (or /var/lib/setserial/autoconfig that you "edit" by simply using the setserial command in the normal way and what you set using setserial is saved in the serial.conf configuration file. The serial.conf file should be consulted when the setserial command runs from a start-up file. Your distribution may or may not set this up for you.
There are two different ways to use setserial depending on the options you give it. One use is used to manually tell the driver the configuration. The other use is to probe at a given address and report if a serial port exists there. It can also probe this address and try to detect what IRQ is used for this port.
Even with modern kernels, setserial is sometimes needed if the driver fails to detect the serial port, or if you have very old hardware.
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