Re: [PATCH -mm] 1/2: MMCONFIG: validate against ACPI motherboard resources

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Olivier Galibert wrote:
On Tue, May 29, 2007 at 10:03:32PM -0600, Robert Hancock wrote:
-Validate that the area is reserved even if we read it from the
chipset directly and not from the MCFG table. This catches the case
where the BIOS didn't set the location properly in the chipset and
has mapped it over other things it shouldn't have.
Just for the record, I still fundamentally disagree with that part.
You're not catching what you think you're catching, since the chipset
tells you what it is going to decode as mmconfig, no matter what is
connected to it.
But we don't - not in the case where it's overlapped some other area
with the MMCONFIG region. We saw a case of this on some of the Intel
boards, where the MMCONFIG is a 128MB area at 0xf0000000, and when
sizing the BARs on a PCI Express video device with a 256MB region, it
ended up being located momentarily at f0000000-ffffffff, which
overlapped the MMCONFIG area. That caused MMCONFIG to stop working, so
apparently on that chipset, PCI Express devices connected to the
northbridge have a higher decode priority than the MMCONFIG area.
If the BIOS is so screwed up that this becomes an issue, I don't think
we can sanely try to use the table, since we can't anticipate all the
potential problems that might result.
Robert Hancock      Saskatoon, SK, Canada
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