linux-kernel - Re: 2.6.32 regression (bisected): Video tearing/glitching with T400 laptops

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Date:	Tue, 13 Oct 2009 12:14:26 -0700
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	Theodore Tso <tytso@....edu>
Cc:	"Carlos R. Mafra" <crmafra2@...il.com>,
	Eric Anholt <eric@...olt.net>, linux-kernel@...r.kernel.org,
	Keith Packard <keithp@...thp.com>
Subject: Re: 2.6.32 regression (bisected): Video tearing/glitching with T400
 laptops

On Tue, 13 Oct 2009 15:00:55 -0400
Theodore Tso <tytso@....edu> wrote:

> Thanks, should I apply this on top of your previous patch, or on a
> completely virgin 2.6.32-rc3 tree?

Either way should be fine, since the previous patches don't appear to
be helping (they shouldn't hurt either).

> I don't know if this helps, but the amount of tearing seems to be
> roughly proportional to how many "white" pixels are on the screen.
> There isn't much tearing if I just have my (brown) Ubuntu 9.04 default
> background image.  There is a bit more tearing on the virtual desktop
> once I open an 80x52 black-on-white gnome-terminal window, so that 45%
> of my widescreen has white pixels due to the backgrouin of the
> gnome-terminal.
> 
> On the virtual desktop where my firefox browser is opened, the
> tearing/glitching is much more frequent.  And where the
> tearing/glitching is seems to be be roughly related to where the mouse
> cursor happens to be.  (Usually starting at the horizontol row of
> pixels where the mouse is going down towards the bottom of the screen;
> although sometimes if the mouse is very close to the bottom of the
> screen, there is some tearing at the top of the screen as well.)
> 
> Does this description help at all?  Would a video clip of the
> tearing/glitching be useful?

Thanks for the description, it matches what I've seen on Eric and Ian's
machines, though I can't reproduce it myself.

According to the chipset team that form of display corruption is likely
related to RAM self-refresh... Sounds like the display plane isn't
getting its memory requests serviced fast enough when in self-refresh
mode, which might mean we have to program the self-refresh watermarks
more aggressively on GM45.

-- 
Jesse Barnes, Intel Open Source Technology Center
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