Re: [PATCH] x86: Reserve legacy VGA MMIO area for x86_64 as well as x86_32

[Bjorn Helgaas]

On Wednesday 07 April 2010 05:22:43 pm Yinghai wrote:
> 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 http://lkml.org/lkml/2010/4/6/375
> >>>
> >>> 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...

Why is this different for 64-bit vs 32-bit?  Can you point me to any
references where I can learn about this?

Bjorn
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