linux-kernel - Re: [Bug 10843] Display artifacts on XOrg logout with PAT kernel and VESA framebuffer

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Date:	Sun, 14 Sep 2008 15:25:20 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Frans Pop <elendil@...net.nl>
Cc:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"arjan@...ux.intel.com" <arjan@...ux.intel.com>,
	"jbarnes@...tuousgeek.org" <jbarnes@...tuousgeek.org>
Subject: Re: [Bug 10843] Display artifacts on XOrg logout with PAT kernel
	and VESA framebuffer


* Frans Pop <elendil@...net.nl> wrote:

> On Saturday 13 September 2008, Pallipadi, Venkatesh wrote:
> > >We have too many entires in PAT list due to RAM pages being marked
> > >UC by drivers. Unfortunately, there are no quick fixes that can fix
> > >this for 2.6.27. However, we are aware of the problem here and
> > >working on a more complete fix for this. We should have the patch
> > >for it soon.
> >
> > Can you try the patch here
> > http://www.ussg.iu.edu/hypermail/linux/kernel/0809.1/2074.html
> > And report back whether that resolves the issue.
> 
> Yes, that solves the issue. The display is now free of artifacts 
> again, both on logout and when I switch users in X. The 
> pat_memtype_list looks a lot more sane too (see attachment).
> 
> So it _was_ a regression caused by pat itself after all, and not the 
> result of incorrect memory handling in the framebuffer code. Could you 
> take over the bug report #10843 in bugzilla (it is currently assigned 
> to the framebuffer people) and ensure it gets closed once the patch 
> gets accepted in Linus' tree?

ok, since those patches are only supposed to improve performance, it 
would be nice to know why this fixes the display artifacts. They were a 
rather long-living bug and we'd like to avoid such bug patterns in the 
future.

or is it the timing effect? Too slow programming of the GX chip causes 
artifacts? (but i think this is not very likely)

	Ingo
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