Messages in this thread | | | Subject | Re: [PATCH] Don't touch BARs of host bridges | From | Benjamin Herrenschmidt <> | Date | Sat, 11 Dec 2004 08:25:04 +1100 |
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On Fri, 2004-12-10 at 13:11 +0000, Maciej W. Rozycki wrote:
> Well, some of these bridges may be used for peripheral devices (option > cards) built around a CPU, typically after reprogramming the class code to > something corresponding to their actual function. Why should the address > decoder circuitry suddenly change in this case?
To stay in the PCI spec ? :) They would need at least a way to "lock" the BARs.
> Also even in the "host mode" another device may wish to examine what > resources have been reserved by the host bridge (unlikely, I admit, but > in principle why not?).
Very unlikely.
> > was well :) So I agree, that would be useful to skip them. I'm not sure > > about PCI_CLASS_NOT_DEFINED tho ... > > These are pre-2.0 PCI devices -- from before the detailed classification > was agreed upon. AFAIK, just a couple of them exist -- I can name: > Intel's 82424 and 82425 families of i486 host bridges, their 82375 family > of PCI-EISA bridges and their 82378/9 family of PCI-ISA bridges (also used > in a few DEC Alpha systems). There are probably a handful of other chips, > all of them about ten years old. Our i386 and ppc resource managers skip > over them as well and I suppose this is a safe default. If any of them > needs BAR setup (none of these Intel ones), it can be added explicitly by > means of its vendor:device ID.
Ok.
Ben.
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