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    SubjectRe: [PATCH] x86: Reserve legacy VGA MMIO area for x86_64 as well as x86_32
    On 04/09/2010 03:51 PM, Alan Cox wrote:
    >> Why is this different for 64-bit vs 32-bit? Can you point me to any
    >> references where I can learn about this?
    >
    > IMHO its wrong for both
    >
    > You can only reserve the region in question if you actually have a VGA
    > device and mappings present.
    >
    > It's wrong for non PCI systems
    > It's wrong for legacy ISA systems with monochrome video/no video
    > It's wrong for several embedded platforms.
    > It's wrong if PCI isn't your root bridge
    >
    > Basically the reservation is the wrong way to fix it. A much saner way to
    > fix it would be to simply keep a list of address ranges not to use for
    > PCI device relocation. For I/O ports of course we just fix up the PCI
    > resources of the device to list them as we discover it (IDE legacy).
    >
    > You don't want to put anything at the VGA address that needs assigning an
    > address. That is *totally* different to the question of whether you want
    > to believe the space is 'reserved'. If something is at that address then
    > presumably the firmware knows what it is doing. If a device driver wishes
    > to reserve that address it's doing so with more information, later in
    > boot so should be allowed to.

    That's what I mean with reserved, I'm using the term in the
    E820_RESERVED sense. As in "don't put anything there without it being
    an explicit assignment".

    -hpa


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