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Subject: Re: [patch 2.5] 2-pass PCI probing, generic part
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Linus Torvalds <torvalds@transmeta.com>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>,
       Alan Cox <alan@lxorguk.ukuu.org.uk>,
       Grant Grundler <grundler@cup.hp.com>, Paul Mackerras <paulus@samba.org>,
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       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       greg@kroah.com
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On Thu, 2003-01-09 at 23:16, Linus Torvalds wrote:
> On Fri, 10 Jan 2003, Ivan Kokshaysky wrote:
> >
> > Note that in most cases PCI-PCI bridges can be safely excluded from
> > pci_read_bases() simply because they have neither regular BARs nor
> > ROM BAR (even though PCI spec allows that).
> 
> This might be a good approach to take regardless - don't read pci-pci 
> bridge BAR (or host-bridge BAR's for that matter), simply because 
> 
>  (a) bridges are more "interesting" than regular devices, and disabling 
>      part of them might be a stupid thing.
>  (b) we're generally not really interested in the end result anyway

I completely agree. For example, I have already a bunch of cases where I
have to explicitely "hide" the host bridge from linux PCI layer as those
have BARs that mustn't be touched. A typical example is the 405gp
internal PCI host. It has a BAR that represents the view of system RAM
from bus mastering PCI devices. Of course, the kernel doesn't understand
that and tries to remap it away from 0 where it belongs ;)

Ben.

-- 
Benjamin Herrenschmidt <benh@kernel.crashing.org>
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