Re: [Bug #15124] PCI host bridge windows ignored (works withpci=use_crs)

From: Jesse Barnes
Date: Tue Jan 26 2010 - 13:35:33 EST

On Tue, 26 Jan 2010 10:21:29 -0800
Yinghai Lu <yinghai@xxxxxxxxxx> wrote:

> On 01/26/2010 10:16 AM, Linus Torvalds wrote:
> >
> >
> > On Tue, 26 Jan 2010, Bjorn Helgaas wrote:
> >>
> >> which IS big enough, and we know the bridge is in fact forwarding the
> >> [mem 0xd0000000-0xdfffffff 64bit pref] region, because the Radeon works
> >> when Jeff boots with "pci=use_crs".
> >
> > I bet it's a subtractive decode thing. Sure, it could be just another
> > undocumented range register (does anybody have the datasheet for that
> > thing?) but Intel tends to often have subtractive decode.
> >
> > That system in question has three PCI express root ports, but two of them
> > have IO and memory disabled according to the lspci info. So maybe it's as
> > simple as that "I/O Hub PCI Express Root Port 7" just catching anything
> > that nobody else does, and the single IOH host chip doing the same?
> >
> >> I think we should remove intel_bus.c before .33. It's breaking boxes
> >> and we don't know how to fix it. Even if we do find out how to fix it,
> >> I think we should move toward using _CRS instead, because that's what
> >> Windows uses and it's an easy way for the firmware to tell us about
> >> platform quirks.
> >
> > I suspect that for 33 it is indeed best to just revert. But somebody is
> > bound to have information on how the actual hardware works. Yinghai?
> I have asked intel if there is any bit that could be enabled the routing.
> there is no info about for their documentations.

I could probably dig something up in our confidential database, but this
is the main problem with intel_bus.c. It'll always be behind with _CRS
provides. Sure _CRS may be wrong sometimes, but it'll always work well
enough to bring Windows up, so we ought not to ignore it.

The underlying problems with our _CRS support still aren't fixed
though, so switching that on for 2.6.33 isn't an option.

Jesse Barnes, Intel Open Source Technology Center
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