Date: Tue, 7 Apr 2015 14:34:57 +0200
From: Borislav Petkov <bp@suse.de>
To: Aravind Gopalakrishnan <aravind.gopalakrishnan@amd.com>
Cc: Ingo Molnar <mingo@kernel.org>, tglx@linutronix.de, mingo@redhat.com,
        hpa@zytor.com, x86@kernel.org, bhelgaas@google.com,
        linux-kernel@vger.kernel.org, Suravee.Suthikulpanit@amd.com,
        joro@8bytes.org
Subject: Re: [PATCH] x86, aperture: Check for GART before accessing GART
 registers
Message-ID: <20150407123457.GA3681@pd.tnic>
References: <1427898728-3434-1-git-send-email-Aravind.Gopalakrishnan@amd.com>
 <20150402100135.GA5210@gmail.com>
 <551D661D.3030000@amd.com>
 <20150402160634.GB8045@gmail.com>
 <551D6CF5.1010604@amd.com>
 <20150402165356.GE4579@pd.tnic>
 <551D7695.2010509@amd.com>
 <20150402171705.GF4579@pd.tnic>
 <20150402181903.GA8723@gmail.com>
 <5523125E.2010605@amd.com>
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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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