blank external DVI on Thinkpad T40

[Alex Deucher]

On Wed, Feb 25, 2009 at 2:12 PM, Gilad Arnold <arnold at cs.berkeley.edu> wrote:
> Hi,
>
> 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,
> etc).
>
> My configuration:  Xorg server 1.3.0.0-r6 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!

Sounds like display underflow.  Try disabling the LVDS if you aren't
using it.  Another option is to increase the priority of the display
controllers:

Option "DisplayPriority" "HIGH"

Alex