Re: [RFC] Runtime allocation of PCI resources

From: Matthew Garrett
Date: Mon Jun 11 2007 - 13:41:37 EST

On Mon, Jun 11, 2007 at 08:11:24PM +0200, Andi Kleen wrote:
> Matthew Garrett <mjg59@xxxxxxxxxxxxx> writes:
> > BIOS authors don't always program all the features of hardware. This is
> > often the case for Intel IDE controllers, which are usually able to run
> > in AHCI mode but are rarely configured to do so. Reprogramming them is
> > easy enough other than the requirement for some MMIO space. If the BIOS
> > hasn't allocated this, it's necessary for us to do so manually.
> Traditionally we've had bad experiences forcing hardware to do something
> the BIOS didn't consider. e.g. occasionally the BIOS has good reasons
> to not allow it; maybe it knows about some errata or other problem
> the kernel doesn't.

AHCI is generally disabled because it makes Windows insanely difficult
to install. I'm not aware of any hardware issues in this case.

> I tried something similar some time ago for the IOMMU aperture.
> It turned out that some systems put something into the e820 holes
> and didn't boot anymore if you put something else in there.
> Your resource allocation will just do that.
> You might be lucky because your resources are typically
> small (IOMMU aperture was 64+MB) or you might not.

Hm. Yes, that would be a problem (sigh BIOS authors).
Matthew Garrett | mjg59@xxxxxxxxxxxxx
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