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

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Message-ID: <20091015022645.GA8286@mit.edu>
Date:	Wed, 14 Oct 2009 22:26:45 -0400
From:	Theodore Tso <tytso@....edu>
To:	Jesse Barnes <jbarnes@...tuousgeek.org>
Cc:	"Carlos R. Mafra" <crmafra2@...il.com>,
	Eric Anholt <eric@...olt.net>, linux-kernel@...r.kernel.org,
	Keith Packard <keithp@...thp.com>,
	Chris Wilson <chris@...is-wilson.co.uk>
Subject: Re: 2.6.32 regression (bisected): Video tearing/glitching with
	T400 laptops

On Wed, Oct 14, 2009 at 02:22:52PM -0700, Jesse Barnes wrote:
> On Tue, 13 Oct 2009 12:14:26 -0700
> Jesse Barnes <jbarnes@...tuousgeek.org> wrote:
> > 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.
> 
> Ok, like any good bug there was more than one thing wrong:
>   - we weren't setting up a fence for the object before enabling FBC.
>     Chris caught this and posted a patch to
>     intel-gfx@...ts.freedesktop.org titled "drm/i915: Install a fence
>     register for fbc on g4x" (attached for convenience)
>   - turns out we *do* need to set watermarks on G4x, despite some hw
>     documentation indicating otherwise, patch for that attached
> 
> Hopefully with these two you'll have a solid display and some power
> saving!

With these two patches (and none of your prior ones) applied to
2.6.32-rc3, things are definitely better.  I'm still seeing a few
glitches (one as mutt was loading my Maildir inbox) and one as I was
typing this message in emacs, but it's at best one minor every 5-10
minutes.  It's rare enough to be at most a wee bit distracting (*lots*
better than before), and I can see the power savings.

If I need to live with a display glitch every 5-10 minutes or so to
get better power savings, I'll take it....

						- Ted
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