linux-kernel - Re: [PATCH 2/2] x86: add early quirk for reserving Intel graphics stolen memory v3

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Message-ID: <20130726101221.016e93b5@jbarnes-desktop>
Date:	Fri, 26 Jul 2013 10:12:21 -0700
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	mingo@...e.hu, tglx@...utronix.de, torvalds@...ux-foundation.org
Subject: Re: [PATCH 2/2] x86: add early quirk for reserving Intel graphics
 stolen memory v3

On Fri, 26 Jul 2013 09:58:45 -0700
"H. Peter Anvin" <hpa@...or.com> wrote:

> On 07/25/2013 09:37 AM, Jesse Barnes wrote:
> > Systems with Intel graphics controllers set aside memory exclusively for
> > +	/*
> > +	 * Almost universally we can find the Graphics Base of Stolen Memory
> > +	 * at offset 0x5c in the igfx configuration space. On a few (desktop)
> > +	 * machines this is also mirrored in the bridge device at different
> > +	 * locations, or in the MCHBAR.
> > +	 */
> 
> This comment makes me nervous.  It isn't clear to me if it is saying:
> 
> - All igfx devices has the graphics base at 0x5c, a few have it in
>   other places, too (which doesn't matter, we can use 0x5c anyway), or
> - Most igfx devices have the graphics base at 0x5c, some don't, and we
>   hope and pray we're not on one of those systems because we're not
>   checking.
> 
> I assume it is the former, but it really needs to be phrased better.

I mostly copied it from the driver where we had some other ways of
finding it too.  For the PCI IDs listed, we can always use 0x5c.  I'll
fix the comment.

-- 
Jesse Barnes, Intel Open Source Technology Center
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