linux-kernel - Re: [git head] Should X86_PAT really default to yes?

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Date:	Mon, 5 May 2008 19:32:40 +0200
From:	Frans Pop <elendil@...net.nl>
To:	Jesse Barnes <jesse.barnes@...el.com>
Cc:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	linux-kernel@...r.kernel.org, "Ingo Molnar" <mingo@...e.hu>,
	"Packard, Keith" <keith.packard@...el.com>,
	"Yinghai Lu" <yhlu.kernel@...il.com>
Subject: Re: [git head] Should X86_PAT really default to yes?

Sigh. This is going to get complex...

On Monday 05 May 2008, Jesse Barnes wrote:
> > > If so, it might not be a PAT issue but just a different memory layout
> > > or something (and therefore it would really just be a cosmetic bug in
> > > the X driver).
> >
> > The artifacts may not be a PAT issue directly, but it is a clear
> > regression for me as I currently have a nice clean screen when X shuts
> > down. I'm also 100% sure that it is caused by enabling PAT. A kernel
> > with same config and only PAT disabled does not show the artifacts.
> >
> > Would you like me to file a bug against X for these artifacts?
> > If so, against what component? The i810 driver or the server?
>
> I suspect an i810 driver bug is being uncovered here, since we do have
> transient VT switch corruption on some other platforms (we're just
> exposing our chip reprogramming on the screen, rather than keeping it off
> the whole time).  But there could also be something PAT specific going
> on, I'll have to walk through those code paths...

I suspect it could be vesafb/fbcon related instead. Normally I boot my 
system with 'quiet vga=791', i.e. with vesafb. I then see the artifacts.

When I boot without 'vga=791', I hit another, unrelated regression (which 
I'll report separately) [1].

When I boot with 'video=vfb:off', I do _not_ get the artifacts when X exits.

Note that the "expected mapping type" errors remain the same both with and 
without framebuffer console.


> Oh the messages should be removed or somehow minimized, I agree.  I'm
> just not sure if the other bug is serious enough to block PAT by default
> yet, but either way we should fix the bugs!

OK. Thanks. Guess you've also seen "Xorg crash with xf86MapVidMem error" 
that turned out to be due to PAT: 
http://www.gossamer-threads.com/lists/linux/kernel/915300 ?

Cheers,
FJP

[1] Short version of this unrelated issue.
If I boot without vga=791 the console stops being updated after PCI probes.
At first I thought this was #9310, but this time it's unrelated to the 
config option mentioned there. Symptoms are awfully similar though.
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