I have a thinkpad t42 with the ATI mobility 7500. When I plug my laptop into the dock the radeon driver never displays anything on the external monitor. This is with the laptop case shut, so the internal LCD is inactive. I can only get the external display to work using the fbdev Driver, and then only at 1024x768. My external monitor is a hp L1925 lcd 1280x1024 connected via DVI to the docking station. I'll attach the Xorg.log file. This is using Mandrake 10.1 and both it's xorg 6.7.0 and 6.8.1 rpms from the offical DVD.
Created attachment 1437 [details] Xorg 6.7.0 log file for Radeon driver
I think you need to change the active ports in the bios. change it to DVI+LCD as I recall.
I'll look into the bios thing, but I'd guess it's unlikely to help since the fbdev driver can output to the display, while the radeon driver cannot. I should've mentioned before when trying to run the radeon driver the external LCD does flash black a few times before X fails completely.
Tried the DVI+LCD bios change. Exactly the same as before. All boot messages show on external display just fine, and the text consoles work fine at 1024x768. Just not X with the radeon driver. It looks like X doesn't actually die, the process is still running it just doesn't show anything on the screen.
Got it working finally. I had to uninstall the ATI driver mandrake installs by default, and upgrade to their Xorg 6.8.1 packages. Only then did a Xorg -configure work, and provide a configuration that works. Also works fine with gentoo's xorg 6.8.0. I never got xorg 6.7.0 to work.
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