Resolution problem with AMD Radeon 5450/6350 and Dell U3011

[Johan Mazel]

Hi
I am trying to use a Dell U3011 (30 inches IPS screen) on a Dell
Optiplex 990 with an AMD HD 5450/6350.
I am using Debian Testing and Ubuntu 12.10 with Xorg's ATI driver.
The respective xserver-xorg-video-radeon package versions for these
two OSes are: 1:6.14.4-5 and 1.6.99.99~git20120913.8637f772-0ubuntu1.

Theoretically, the HD5450 is able to display the screen's native
resolution (2560x1600) according to
http://www.amd.com/us/products/desktop/graphics/ati-radeon-hd-3000/hd-3400/Pages/ati-radeon-hd-3400-specifications.aspx
provided that a dual-link DVI cable is used, which is the case.
Unfortunately, the biggest available resolution is 1600x1200 on Debian
Testing and 1920x1200 for Ubuntu 12.10.

I think there is a discrepancy between what Xorg probes through the
graphic card as the biggest resolution available (1600x1200, starting
line 438 in Xorg.0.log_debian_xorg) and what is actually announced by
the monitor (2560x1600, eg.: line 587 (and further) in
Xorg.0.log_debian_xorg).
This discrepancy is also present in Ubuntu's Xorg log files.

I am guessing that Ubuntu uses a slightly newer version of the driver
and therefore handle slightly better the resolution.
However, I have no idea regarding the cause of this discrepancy.
Thanks for your time.
Johan
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