Resolution for external monitor missing in list for DFP1

[Jesusfreak]

I use a Thinkpad R500 (1680x1050) with a docking station and an external monitor (1920x1200) attached to it. When I boot the Thinkpad and later attach it to the docking station, then the highest resolution in the arandr DFP1 list is 1600x1200. This means I have to reboot the system, as a boot right from the docking station gives me the 1920x1200 I need for the external monitor.

I also want to point out that this has worked well for a long time, until I had to reinstall my Xubuntu a couple of weeks ago.

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: arandr 0.1.4-1
ProcVersionSignature: Ubuntu 3.0.0-16.28-generic 3.0.17
Uname: Linux 3.0.0-16-generic x86_64
NonfreeKernelModules: fglrx
ApportVersion: 1.23-0ubuntu4
Architecture: amd64
Date: Sun Feb 26 15:47:43 2012
EcryptfsInUse: Yes
InstallationMedia: Xubuntu 11.10 "Oneiric Ocelot" - Release amd64 (20111012)
PackageArchitecture: all
ProcEnviron:
 LANGUAGE=en_US:en
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: arandr
UpgradeStatus: Upgraded to oneiric on 2012-02-08 (17 days ago)

[chrysn (chrysn)]

please open a terminal and run the following command in a situation when arandr produces erroneous results:

xrandr --verbose > /tmp/xrandr.out

and submit the file /tmp/xrandr.out to this bug report, then i can have a closer look at the situation.

[chrysn (chrysn)]

this is not exactly arandr's fault, but i think i can help anyway (an explanation follows, if you just need to fix it go to the last paragraphs):

when the x server starts, it figures out how large to make the "Virtual", the theoretical maximum area. in arandr, the virtual is shown as the dark gray area.

when your external monitor is not connected, the largest horizontal extension of all the monitors the x server sees at startup is 1680 (your laptop monitor's width), and it choses to make the virtual 1680x1680 in case you want to rotate your monitor.

when the external monitor gets later connected, even though it announces it resolutions correctly (as seen in the EDID_DATA block), the x server only offers the resolutions that would fit in the existing virtual. everything larger gets dropped, and 1600x1200 is the largest that fits.

when the external monitor is connected at startup, the x server sees the need for the larger screen, and allocates the virtual appropriately.

as a workaround, you can give x an explicit virtual size to allocate. depending on how you use your displays, this could be 1920x1200 (if you only use either monitor), 3600x1200 (if you want them side by side), or 3600x3600 (if you want to use all possible combinations, including rotated monitors) or even higher given you could connect even more monitors. create an /etc/X11/xorg.conf with the following contents:

Section "Screen"
 SubSection "Display"
  Virtual 3600 1200
 EndSubSection
EndSection

(you may or may not have to integrate that into an existing xorg.conf, depending on your configuration)

[chrysn (chrysn)]

re-assigning this to fglrx because the choice of the virtual size drastically reduces the benefit of xrandr, basically to choosing whether or not to mirror the primary output.

for comparison, on a similar laptop with an intel gm965 graphics card, it defaults to 8k times 8k.

[Jesusfreak (launchpad-bikelab)]

Adding the SubSection solved the problem. Thanks a lot.