Re: [PATCH] Don't touch BARs of host bridges

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

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.