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    SubjectRe: fixing "pci=use_crs"
    On Wed, 2009-09-23 at 21:42 -0700, Yinghai Lu wrote:
    > On Wed, Sep 23, 2009 at 8:21 PM, Bjorn Helgaas <> wrote:
    > > On Wed, 2009-09-23 at 16:28 -0700, Yinghai Lu wrote:
    > >> On Wed, Sep 23, 2009 at 4:23 PM, Bjorn Helgaas <> wrote:
    > >
    > >> > P.S. Yinghai, you posted some patches earlier dealing with "only one
    > >> > HT chain." You apparently have some insight into what's going on here,
    > >> > but unfortunately, the changelogs mean absolutely nothing to me. Can
    > >> > you give me any clues?
    > >>
    > >> which commit?
    > >>
    > >> normally we only need to have split root resource into several pieces
    > >> when we have two HT chains or other io chains...
    > >
    > > I meant the patches here:
    > >
    > >
    > > My opinion is that ACPI is there to give us an abstract description of
    > > the machine, and we shouldn't have to introduce knowledge like "this
    > > machine has two HT chains" or add checks in amd_bus.c about
    > > "pci_root_num <= 1".
    > >
    > > But maybe if I knew what an HT chain was and why you think it affects
    > > the description returned by _CRS, it would give me a clue about how to
    > > deal with this in a generic way.
    > we could use _CRS, but lots of BIOS just provide messed up resources
    > in _CRS to OS.

    We do have to assume there are BIOS defects here, but in most cases, I
    look for Linux deficiencies first. I'm assuming (without real evidence)
    that Windows does look at the _CRS, so the worst BIOS defects should be
    weeded out by Windows testing.

    > for example, the HW conf register does have mmio high range there, but
    > _CRS doesn't report them.

    On Larry's box, _CRS reports *more* ranges than Linux was prepared for.
    This would be a bug in the other direction, where _CRS reports *less*
    than it should.

    > thought we can use whilelist to use _CRS for them.

    I'm opposed to a whitelist for this issue because it means we have to
    continually update the whitelist for new, correctly working machines.
    If we can't figure out anything better, we could use a date-based
    blacklist (ignore _CRS for all machines older than today).

    But first, we have to establish that there really is a requirement to
    look at _CRS, then have a good try at making Linux smart enough to deal
    with whatever it finds.


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