blank external DVI on Thinkpad T40

Gilad Arnold arnold at
Wed Feb 25 11:12:34 PST 2009


I've been running Xorg with Gentoo Linux on my T40/T41 for a while now.
In the past I was able to use my DVI monitor to its full 1920x1200
resolution with hardware acceleration using the open-source radeon
driver (single output mode, the laptop's LCD was disabled). However,
since the upgrade to Xorg 1.3 with the new XRandR capabilities, I'm
having trouble getting my DVI monitor to work properly.

Specifically, xrandr is now reporting 4 different connections: LVDS (my
laptop's LCD), VGA-0, DVI-0 and S-video. With the LVDS running at
1400x1050, my DVI stays blank (not sure if it is getting a signal at
all) at any resolution beyond 1680x1050, namely 1600x1200 or 1920x1200.
Moreover, even at 1680x1050, my picture is not very "stable": at times
of heavier video / CPU / memory usage (e.g. when scrolling a web-browser
page with the mouse, or when running a CPU/memory intensive program) my
DVI would go blank; sometimes picture is restored after a second or two,
but sometimes it stays blank and has to be reset (the '--off' option in
xrandr, then on again). Only at 1400x1050 (same as the LVDS resolution)
do I get a steady and reliable performance from my DVI.  Clearly, this
defeats the purpose of using an external monitor at all... ;-)

Some more details: the VGA-0 port works fine with the same monitor
(using the RGB port) and I am able to use the 1920x1200 mode flawlessly.
The picture quality is inferior to DVI, however, so this is not an ideal
configuration as well.

Inspecting the Xorg log file I cannot spot anything peculiar that might
provide any hint: the radeon driver detects the hardware correctly and
is able to start it with hardware acceleration. I did not try switching
to fglrx yet.

My suspect is that something is quirky between the xrandr module and the
radeon driver: either the former is assuming something about the
capabilities of the latter that cannot be supported (e.g. running 3
displays with high resolution at the same time), or the latter is not
managing the hardware correctly (e.g. video memory conflicts/overflows,

My configuration:  Xorg server with Xorg ATI Drivers (radeon)
6.10.0. I'm using the Xorg DRM module.  lspci reports a Radeon R250
(Mobility FireGL 9000) rev 02 and the Xorg log file confirms this.

I would appreciate any hints on where I should look and what to check.
If my configuration is inherently not supported by the newer Xorg, then
I might rollback to an older version (although I do like the new xrandr
capabilities). Also, if fglrx works better then that's an option
(although I like it much less that using the open-source driver).

Thanks for your help!


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