linux-kernel - Re: Linux 2.6.39-rc3

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Date:	Thu, 14 Apr 2011 17:34:46 -0400
From:	Alex Deucher <alexdeucher@...il.com>
To:	Joerg Roedel <joro@...tes.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>, Yinghai Lu <yinghai@...nel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	dri-devel@...ts.freedesktop.org,
	Thomas Gleixner <tglx@...utronix.de>, Tejun Heo <tj@...nel.org>
Subject: Re: Linux 2.6.39-rc3

On Thu, Apr 14, 2011 at 5:09 PM, Joerg Roedel <joro@...tes.org> wrote:
> On Thu, Apr 14, 2011 at 10:28:43AM -0400, Alex Deucher wrote:
>> On Thu, Apr 14, 2011 at 4:56 AM, Joerg Roedel <joro@...tes.org> wrote:
>> > And this makes a difference, with this change on-top of -rc3 the box boots
>> > fine. So there seems to be some dependency between the GART base and the GTT
>> > base even when they are in different address spaces.
>> >
>> > Alex, can you comment on this?
>>
>> As Dave said, they are completely different addresses spaces.  You
>> could put the GPU aperture at 0 if you wanted (in fact we do on some
>> chips).  Perhaps there's some strange interaction with the nb gart
>> since the nb gart on that chipset was designed to be used for graphics
>> and the rs780/880 can be configured to use an agp aperture.
>> Unfortunately, I'm not that familiar with the nb gart.
>
> Actually, the nb gart is part of the cpu. It is part of the cpu north
> bridge and can translate io and cpu accesses. In fact, it is a remapper
> of physical memory addresses.

I know what it's for.  In the IGP graphics chip is also part of the
north bridge, but it may not be related at all.

>
> The problem seems to be related to specific gpu chips. On another
> notebook with an hd3000 card gtt and the nb gart aperture are both on
> 0xa0000000 too but the box works fine. I havn't tested with an hd5000
> yet. The failing notebook has an hd4200 mobility.

What exact model is the hd3000?   Is it IGP GPU or a discrete GPU?  It
it's an IGP, it's identical to the hd4200 programming-wise.

>
> Btw. what happens if the gpu accesses an unmapped address in the gtt
> range?

It's redirected to a dummy page.

Alex
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