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SubjectRe: Hard coding default COM3/4 IRQ.
   Date: 	Fri, 28 May 1999 13:54:06 -0400 (EDT)
From: "Mike A. Harris" <mharris@ican.net>

Could someone please let me know how to change the _DEFAULT_ COM3
and COM4 IRQ for the linux kernel? I could probably find it
easily enough by hunting through the source, but if someone could
just let me know it would be a bit easier.

You can do it by editing the table in include/asm/serial.h

Also, it would be nice if this were a CONFIG option. Now I know
it is easily rectified in userland by using the setserial
program, and that is how I do it, however with various new
installations out there, I often forget to configure the com IRQ,
and as such the modem wont work.

Put an rc.serial into /etc/rc.d, and that way you don't have to
remember....

Also, why doesn't Linux automatically configure the IRQ on the
COM port? I'm not complaining, however every single installation
of Windows 95 I've seen yet, has miraculously and transparently
configured the COM IRQ. This leads me to believe that there is a
safe and consistent way of determining what IRQ a given COM port
has.

Is there any technical reason for not autoprobing serial IRQ's?
Does a kernel patch to do this exist? Does any of this sound
like it might be possible to throw into 2.2.x? What about 2.3.x?

There is a CONFIG option for doing autodetection of the IRQ,
CONFIG_SERIAL_SHARE_IRQ; you need to answer yes to
CONFIG_SERIAL_EXTENDED to see the extra serial config options. The
problem is that it doesn't always work. I suspect that Linux folk very
often have a lot more random hardware attached to their machines than
Windows folks, and these random ISA bus cards can confuse an
autodetection algorithm.

It works *most* of the time, but even when it fails 0.001% of the time,
if 10% of the people for whom it fails sends me mail, with a 7-10
million user base, that's still a lot of e-mail, and basically, I got
tired of trying to support it. That's why it's off by default, and the
config option is labeled "unsafe", since sometimes the autodetection can
screw up other devices in your systems who really are supposed to have
that irq.

- Ted

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