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

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Date:	Tue, 7 Apr 2015 14:34:57 +0200
From:	Borislav Petkov <bp@...e.de>
To:	Aravind Gopalakrishnan <aravind.gopalakrishnan@....com>
Cc:	Ingo Molnar <mingo@...nel.org>, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, x86@...nel.org,
	bhelgaas@...gle.com, linux-kernel@...r.kernel.org,
	Suravee.Suthikulpanit@....com, joro@...tes.org
Subject: Re: [PATCH] x86, aperture: Check for GART before accessing GART
 registers

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.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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