[Linux-parport] [PATCH 2.6.7] Parallel port detection via ACPI

Adam Baker parport at baker-net.org.uk
Sat Jul 3 16:28:50 EDT 2004

On Saturday 03 July 2004 19:07, Dino Klein wrote:
> ACPI will identify the port either as a standard parallel port (PNP0400),
> or enhanced parallel port (PNP0401). Now, PNP0400 includes SPP and EPP
> modes, while PNP0401 is ECP and ECP+EPP.
> I checked the ouput of the modes detected for the port for every setting in
> the BIOS, and the funny thing I noticed that even when set to SPP, the
> driver listed [PCSPP,EPP], while in EPP it listed [PCSPP,TRISTATE,EPP].
> Perhaps somebody should review the detection code. I can't, because I'm not
> knowledgeable with parallel ports.
Unfortunately I believe the detection code is primarily a trial and error 
thing to see what works best on the wide variety of badly implemented 
chipsets and BIOSes that are out there. My opinion was formed from a 
combination of seeing how things go in the rest of the PC industry and 
reading the driver code.

Maybe we should accept that detection of supported modes will never be perfect 
and provide a mechanism to specify it with a parameter when the driver gets 
it wrong. I realise that is the exact opposite of what you were trying to 
achieve with the ACPI patch but I doubt many people have a wide enough 
variety of hardware to test on to be confident that any changes will make 
things better rather than worse for the majority of users.

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