Message-ID: <5523EDC2.5080206@amd.com>
Date: Tue, 7 Apr 2015 09:46:26 -0500
From: Aravind Gopalakrishnan <aravind.gopalakrishnan@amd.com>
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0
MIME-Version: 1.0
To: Borislav Petkov <bp@suse.de>
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
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> <20150407123457.GA3681@pd.tnic>
In-Reply-To: <20150407123457.GA3681@pd.tnic>
Content-Type: text/plain; charset="utf-8"; format=flowed
Content-Transfer-Encoding: 7bit
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Apr 2015 14:46:29.8489
 (UTC)
X-MS-Exchange-CrossTenant-Id: fde4dada-be84-483f-92cc-e026cbee8e96
X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=fde4dada-be84-483f-92cc-e026cbee8e96;Ip=[165.204.84.222];Helo=[atltwp02.amd.com]
X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BY1PR0201MB0887
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 1360
Lines: 39

On 4/7/2015 7:34 AM, Borislav Petkov wrote:
> 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.
>

Okay. I'll do that and correct the typos Ingo pointed out earlier and 
resend.

Thanks,
-Aravind.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/