Re: wrong number of serial port detected

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From: Bjorn Helgaas <[email protected]>
To: "Jason Dravet" <[email protected]>
CC: [email protected], [email protected]
Subject: Re: wrong number of serial port detected
Date: Fri, 9 Dec 2005 12:54:44 -0700

On Friday 09 December 2005 7:37 am, Jason Dravet wrote:
> The question I have
> is with all of this plug and play stuff in our PCs shouldn't it be possible
> to get the correct number of ports, ask the bios or the pci bus or
> something?

Yes.  ACPI (or even PNPBIOS) should tell us about all the "legacy"
ports, and PCI or other bus enumeration should tell us about all the
rest.

So in theory, if we have some flavor of PNP, we should be able to
ignore all the compiled-in stuff in SERIAL_PORT_DFNS, which is what
leads to the duplicate port detection.  I've considered doing that
(and ia64 already does it), but it would almost certainly break
systems because of BIOS bugs, so I'm not sure it's worth the risk.

I agree that breaking things is bad, but it would be interesting to see what would happen and if anyone complains. A gut feeling is that very few people use more than the two serial ports that come on their motherboards. Where I work out of the 2,500 PCs on campus, only 3 or 4 PCs actually use a serial port. I think this would be a good survey for slashdot. I don't use the serial ports on my PCs. I do use the serial ports on my servers. The serial ports on the servers connect to a digi terminal server. One serial port is the management interface to the server, the other is setup for serial login.

The reason I started this thread is because I wanted to know why/how I was seeing 32 serial ports in /dev when I have 0 enabled on my PC and I have 2 serial ports on my servers. Thanks to the responses I have a better understanding of what is going on.

Having all the extra /dev/ttyS entries is a little different problem.
That is basically so "setserial /dev/ttySx" can be used to work around
the fact that the serial driver doesn't know about all existing devices.
If it did, setserial should be superfluous.  Maybe there'd be a way to
implement that functionality via sysfs and get rid of the extra
/dev/ttyS entries.  That'd be kind of cool.

sysfs is way outside my area of understanding. Anything that moves to a more accurate /dev directory is good in my book.

Thanks,
Jason


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