Re: acpi based pci gap calculation - v3

From: Alok Kataria
Date: Tue Jul 22 2008 - 18:53:16 EST

On Tue, 2008-07-22 at 14:50 -0700, Jesse Barnes wrote:
> On Monday, July 21, 2008 10:59 am Alok Kataria wrote:
> > Hi Jesse,
> >
> > Did you get a chance to try this patch on your box. Let me know what are
> > the values you get now.
> Here's the dmesg from my box with the ACPI gap stuff applied.
> I'm still more inclined to TJ's approach though; it should give us a lot more
> space for PCI devices; though you're right that avoiding conflicts is
> definitely important too...

Hi Jesse,

Thanks for sending the log.

In the log that you sent me, please note the following debug messages
E820_DEBUG: Searching for gap between (0x00000000 - 0x100000000)
E820_DEBUG: Found gap starting at 0xbf000000 size 0x40f00000
Allocating PCI resources starting at c0000000 (gap: bf000000:40f00000)

This is the gap that was allocated by walking just the e820_map

With my changes we query the _CRS resource and get following info
ACPI_DEBUG start_addr 0xf8000000 gapsize 0x00400000 address_length 0x06b00000
end_addr is 0xfeb00000
E820_DEBUG: Searching for gap between (0xf8000000 - 0xfeb00000)
E820_DEBUG: Found gap at start starting at 0x100000000 size 0x07f00000
ACPI_DEBUG start_addr 0xbf000000 gapsize 0x07f00000 address_length 0x31000000
end_addr is 0xf0000000
E820_DEBUG: Searching for gap between (0xbf000000 - 0xf0000000)
E820_DEBUG: Found gap starting at 0xbf000000 size 0x31000000

So there are 2 producer regions one from [0xBF000000 - 0xF0000000] and
another from [0xF8000000 - 0xFEB00000]. That means BIOS has reserved the
area from [0xF0000000 - 0xF7FFFFFF] for some other resource.
If you look a little below in the log there is this

system 00:01: iomem range 0xf0000000-0xf7ffffff has been reserved

So the gap that we had calculated first i.e. from e820_setup_gap did
contain a collision i.e. though a resource was reserved from
[0xf0000000 - 0xf7ffffff] our gap calculation doesn't take that into
account. My patch fixes this issue.

So, IMHO this is a BUG and should be fixed. Please let me know your


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