Resolution problem with AMD Radeon 5450/6350 and Dell U3011

[Alex Deucher]

On Tue, Oct 30, 2012 at 6:35 AM, Johan Mazel <johan.mazel at gmail.com> wrote:
> 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.

While the chip is cable of dual link, dual link is only available if
the oem wired up a dual link DVI connector on your card.  If the oem
used a single link DVI connector, you will be limited to single link
DVI.  I suspect that is what's happening.

Alex