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    SubjectRe: [PATCH] x86: Reserve legacy VGA MMIO area for x86_64 as well as x86_32
    On 04/07/2010 04:05 PM, Bjorn Helgaas wrote:
    > On Wednesday 07 April 2010 04:45:30 pm Yinghai wrote:
    >> On 04/07/2010 02:06 PM, Bjorn Helgaas wrote:
    >>> Currently, we only reserve the legacy VGA area [mem 0xa0000-0xbffff] on
    >>> x86_32. But this legacy area is also used on x86_64, so this patch
    >>> reserves it there, too.
    >>> If we don't reserve it, we may mistakenly move a PCI device to that area,
    >>> as we did here:
    >>> pci_root PNP0A03:00: host bridge window [mem 0xff980800-0xff980bff]
    >>> pci_root PNP0A03:00: host bridge window [mem 0xff97c000-0xff97ffff]
    >>> pci 0000:00:1f.2: no compatible bridge window for [mem 0xff970000-0xff9707ff]
    >>> pci 0000:00:1f.2: BAR 5: assigned [mem 0x000a0000-0x000a07ff]
    >>> as reported by Andy Isaacson at
    >>> I think the fact that the BAR is not within a host bridge window is a
    >>> BIOS defect, and it's now more visible because we have "pci=use_crs" as
    >>> the default. Using "pci=nocrs" is a workaround, because then we won't
    >>> attempt to move the device.
    >> that doesn't look right.
    >> It seem another thread, erission has one model without VGA, and they use that area for other device MMIO.
    >> current for 64bit, We remove [0xa0000, 0x100000) from e820 map if those area is E820_RAM.
    >> in e820_reserve_resources(), kernel will reserve range < 1M according to e820 map.
    >> that is before pci BAR is claimed.
    >> or you can add
    >> boot_params.screen_info.orig_video_isVGA == 1
    >> or double check scan pci tree to see if video is there or not
    > I'm sorry, I can't understand what you're saying.

    for 64 bit, you may check boot_params.screen_info.orig_video_isVGA to see if you need to reserve that VGA range.
    not sure if every bootloader fill that...

    > It seems like you're saying we already have a mechanism to keep us
    > from assigning that VGA range to another device, but obviously it's
    > not working.
    > Maybe it will be clearer if you propose a different patch that prevents
    > us from assigning 0xa0000 to the USB controller.

    when the system only have one peer root bus, can you skip the _CRS for it?


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