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    SubjectRe: [PATCH] x86/PCI: never allocate PCI MMIO resources below BIOS_END
    H. Peter Anvin Mon, 26 Apr 2010 14:12:35 -0700
    >> On Mon, 26 Apr 2010 14:27:56 -0600
    >> Bjorn Helgaas <> wrote:
    >>> I'm a little concerned that those patches are a sledgehammer approach.
    >>> Previously, IORESOURCE_BUSY has basically been used for mutual exclusion
    >>> between drivers that would otherwise claim the same resource. It hasn't
    >>> been used to guide resource assignment in the PCI/PNP/etc core. Maybe
    >>> it's a good idea to also use IORESOURCE_BUSY there, but I'm not sure.
    >>> Right now it feels like undesirable overloading to me.
    >> I guess that's true, removing those regions from the pool entirely
    >> might be better? Or some other, clear way of expressing that the
    >> regions aren't available to drivers. Maybe we need a new IO resource
    >> type for platform ranges.
    >>> I think it also leads to at least one problem: Guenter's machine has no
    >>> VGA but has a PCI device that lives at 0xa0000. The driver for that
    >>> device won't be able to request that region if the arch code has marked
    >>> it busy.
    >> Ah good point, so we'll want another approach at any rate. Yinghai?
    >What we need is to keep track of the areas available for address space
    >allocation by dynamically addressed devices, as distinct from address
    >space that is in use by a kernel-known device. There is an in-between,
    >which one can call "here there be dragons" space, which should never be
    >used for dynamic device allocation, but if a platform device or
    >pre-assigned device uses that space then it should be allowed to be
    >In the case of x86, anything that is E820_RESERVED, *or* in the legacy
    >region (below 1 MB) and is not RAM, is "here there be dragons" space.
    > -hpa
    Moorestown has a similar situation where one of the PCI devices have a BAR
    below 1MB. Moorestown also has the option not to have VGA.

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