linux-kernel - Re: [PATCH] disable CPU side GART accesses

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Message-ID: <21d7e9970810291424g369035d4h562b54c676d49aef@mail.gmail.com>
Date:	Thu, 30 Oct 2008 07:24:34 +1000
From:	"Dave Airlie" <airlied@...il.com>
To:	bob.montgomery@...com
Cc:	"Yinghai Lu" <yinghai@...nel.org>, "Ingo Molnar" <mingo@...e.hu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"vojtech@...e.cz" <vojtech@...e.cz>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"chandru@...ibm.com" <chandru@...ibm.com>,
	"Joerg Roedel" <joerg.roedel@....com>,
	"FUJITA Tomonori" <fujita.tomonori@....ntt.co.jp>,
	"Jesse Barnes" <jbarnes@...tuousgeek.org>,
	"Pavel Machek" <pavel@....cz>, "Andi Kleen" <ak@...ux.intel.com>,
	"Dave Jones" <davej@...hat.com>
Subject: Re: [PATCH] disable CPU side GART accesses

On Thu, Oct 30, 2008 at 6:52 AM, Bob Montgomery <bob.montgomery@...com> wrote:
> On Mon, 2008-10-27 at 23:06 +0000, Yinghai Lu wrote:
>> Bob Montgomery wrote:
>> > On Wed, 2008-10-15 at 23:48 +0000, Ingo Molnar wrote:
>> >> (Cc:-ed the GART folks.)
>> >
>> > Are there any objections to this patch?  The problem has been reproduced
>> > in 2.6.18 and 2.6.27, so existing changes in the gart code have not
>> > addressed it.
>>
>> better to have someone with amd system + 8g ram + agp adapter to verify it...
>>
>> YH
>
> Good idea.
>
> I don't think HP made a system with opteron and agp, so I haven't found
> a system here to test.  But I did see that there have been non-HP
> motherboards from several years ago that advertised opteron with agp.
> Anyone running that type of system?
>
> The other question is whether AGP graphics on linux for amd64 ever
> expected host translation to work, since setting DisGartCpu is turning
> off host translation.

We have an option in the AGP drivers called cant_use_aperture.

This stops the CPU from using the aperture for most DRI things. I
can't confirm this won't regress working systems
though. The whole AMD GART thing scares me, esp if some of the host
chipsets also have an AGP GART.

Dave.
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