From: "Petr Vandrovec" <VANDROVE@vc.cvut.cz>
Organization: CC CTU Prague
To: "H. Peter Anvin" <hpa@zytor.com>
Date: Wed, 8 Jan 2003 21:49:39 +0100
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Subject: Re: PCI code:  why need  outb (0x01, 0xCFB); ?
Cc: linux-kernel@vger.kernel.org
Message-ID: <CACAEBD1F1C@vcnet.vc.cvut.cz>
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On  8 Jan 03 at 10:52, H. Peter Anvin wrote:
> 
> > 1. which device is at port address 0xCFB?
> 
> Hopefully none.

Actually I'm not sure. This code is here since at least 2.0.28,
and during googling I even found code for direct PCI access
(http://www-user.tu-chemnitz.de/~heha/viewzip.cgi/hs_freeware/gerald.zip/DIRECTNT.CPP?auto=CPP)
which sets lowest bit at 0xCFB to 1 before doing PCI config
accesses and reset it back to original value afterward.

So I believe that there were some chipsets (probably in 486&PCI times)
which did conf1/conf2 accesses depending on value of this bit.
Unfortunately I was not able to confirm this - almost nobody provides
northbridge datasheets from '94 era, even Intel does not provide them
(f.e. Neptune) anymore :-(
                                                Best regards,
                                                    Petr Vandrovec
                                                    vandrove@vc.cvut.cz
                                                    
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