linux-kernel - Re: Weirdness in pci_read

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Date:	Mon, 3 Mar 2008 13:02:14 -0800
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	linux-pci@...ey.karlin.mff.cuni.cz
Cc:	benh@...nel.crashing.org,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Matthew Wilcox <matthew@....cx>
Subject: Re: Weirdness in pci_read_bases()

On Monday, March 03, 2008 12:57 pm Jesse Barnes wrote:
> > Not only iommu's. On lots of platforms, we have the PCI MMIO space
> > mapped 1:N, that is, an access at MMIO location N turns into a PCI cycle
> > with address 0. So outbound PCI is effectively remapped, thus allowing
> > access to things like 0 etc... without punching holes in RAM and without
> > other dirty x86-like tricks.
>
> Right, bus address space is really a separate entity; I was just using
> IOMMUs as an example of that...

Err, wasn't really clear here.  CPU->PCI space and PCI->host space are really 
separate entities... IOMMUs will definitely affect the PCI->host mapping, and 
CPU->PCI mappings can be arbitrarily complex as well, though as you say on 
PCs it's typically just flatly mapped into CPU physical space somewhere.

Jesse
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