Re: [PATCH] x86, aperture: Check for GART before accessing GART registers

From: Borislav Petkov
Date: Tue Apr 07 2015 - 08:37:15 EST

On Mon, Apr 06, 2015 at 06:10:22PM -0500, Aravind Gopalakrishnan wrote:
> >So what happens if !early_pci_allowed() but the GART is present? We'll
> >set amd_northbridges.flags |= AMD_NB_GART, but won't run any of the
> >setup code in aperture_64.c, right? Is that a valid setup?
> It might be a valid setup. But it would work correctly only if BIOS did the
> right thing with setting up aperture space.
> If !early_pci_allowed() and BIOS did not setup aperture correctly, that
> would have caused problems already.
> But it has not been an issue so far right?

I think the right question to ask is:

What are we doing when there's no GART?

So what you probably want to do is:

if (!amd_gart_present())
return -ENODEV;

*before* the compound check.

Now, if we have detected a GART, i.e., amd_gart_present() is TRUE, the
code will behave as it used to behave before.

This should be the least intrusive change going forward IMHO.


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