Re: PCI resource problems caused by improper address rounding

From: Robert Hancock
Date: Tue Dec 18 2007 - 19:20:46 EST


Linus Torvalds wrote:

On Tue, 18 Dec 2007, Chuck Ebbert wrote:

On 12/18/2007 04:09 PM, Linus Torvalds wrote:
I wonder what the heck is the point of that pnp entry. Just for fun, can you try to just disable CONFIG_PNP, and see if it all works then?
pnpacpi=off should work.

PnP is also trying (and failing) to reserve all physical memory.

Yeah, that really is a pretty confused-looking pnp table thing. But I have absolutely zero idea how PnP is even supposed to work - the whole thing is just a total hack for Windows, afaik.

The sad part is that *normally* the right thing to do about almost any BIOS information is what we do right now: just avoid that magic address range like the plague, because we have no clue what the heck the BIOS is up to. But it looks like in this particular case, some of the problems may arise exactly *because* we avoid that range.

It would be good to know what Windows does. If ACPI is found, does it perhaps just ignore all the PnP entries these days?

Linus

ACPI is where those PnP entries are coming from (on any modern system anyway). They do show up in Device Manager as devices with resources (the one that reserves all of system RAM on my machine is labeled "System board", others like the one that reserves the MMCONFIG aperature are "Motherboard resources" - the name is based on the PNP device ID, I believe).

It could be that Windows is stupid enough that it will map things over top of physical RAM if the BIOS doesn't explicitly reserve it like that. I suspect based on some comments in Microsoft documents that Windows uses the E820 table to figure out where the RAM is, and ACPI/PnP information to figure out where IO mappings are, but may not really combine those two pieces of information into one overall map like Linux does, which would explain why it needs to reserve all physical RAM..

(As mentioned in another post, I would guess the BIOS is reserving that memory range since it's the MMCONFIG aperture..)

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Robert Hancock Saskatoon, SK, Canada
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