Attempting to do dual-head with ATI Mobility Radeon 7500 can't go above 640x480

[Jeremy Visser]

Binary package hint: xserver-xorg-driver-ati

I have an ATI Mobility Radeon 7500 that works beautifully with a dual-head setup in Windows Vista and XP.

With the laptop screen on 1024x768, external VGA monitor on 1280x1024 -- it all works beautifully. Under Windows.

Under Linux, for some stupid reason, the maximum total screen size is 1024x1024, which means that any dual-head configuration with resolutions over 640x480 does not work.

I want to run 1024x768 and 1280x1024, which adds up (horizontally) to 2304x1024. This works fine under Windows.

Under Linux, this fails, and it informs me that 2304x1024 is too big, and my screens should fit within 1024x1024.

If I set both monitors to 640x480, they add up to 1280x480 horizontally (the 1280 is bigger than 1024), which again does not work, but if I stack them vertically, the resolution 640x960 fits within 1024x1024.

As you can imagine, being forced to run dual-640x480 displays is completely unacceptable in an operating system that claims to be even remotely user friendly.

This is not the hardware's fault. It is the software's fault entirely, because it works perfectly in Windows, and should be fixed.

[Bryce Harrington (bryce)]

You need to specify the "Virtual" option in xorg.conf to set the max total screen size to something larger. The Screen Resolution tool in GNOME can do this for you automatically or you can edit xorg.conf yourself.

The issue of having to set Virtual at all is a known issue already reported and tracked elsewhere.

[Jeremy Visser (jeremy-visser)]

Thanks for that, Bryce. Indeed, adding a "Virtual 2304 1024" line to xorg.conf allows me to run my monitors alongside each other at full resolution.

However, I would agree with you that having to set Virtual at all is a bug. However, I couldn't find any bugs that seem to mention it.

From what I gather from your comment, the GNOME Screen Resolution tool can set the Virtual property on-the-fly. The reason I didn't discover that is because I run the stock GNOME 2.22 control panel, which is not xrandr 1.2-aware -- not the Ubuntu-provided one, which is aware of multi-monitor setups. Is it possible to do set Virtual with xrandr or radeontool on-the-fly? I couldn't find a way to do it.

[Bryce Harrington (bryce)]

On Tue, Nov 04, 2008 at 11:57:40PM -0000, Jeremy Visser wrote:
> Thanks for that, Bryce. Indeed, adding a "Virtual 2304 1024" line to
> xorg.conf allows me to run my monitors alongside each other at full
> resolution.
>
> However, I would agree with you that having to set Virtual at all is a
> bug. However, I couldn't find any bugs that seem to mention it.
>
> >From what I gather from your comment, the GNOME Screen Resolution tool
> can set the Virtual property on-the-fly. The reason I didn't discover
> that is because I run the stock GNOME 2.22 control panel, which is not
> xrandr 1.2-aware -- not the Ubuntu-provided one, which is aware of
> multi-monitor setups. Is it possible to do set Virtual with xrandr or
> radeontool on-the-fly? I couldn't find a way to do it.

Guess you're on your own in that case. Maybe talk to the GNOME guys.
You can always just add it manually to xorg.conf.

Bryce

[Jeremy Visser (jeremy-visser)]

Probably also a bug is the fact that direct rendering completely fails when Virtual is set. Not even glxgears will run smoothly -- i.e. it only updates once every two seconds or so. Starting a game actually crashes X.