Radeon X300, dual head

Alex Deucher alexdeucher at gmail.com
Sat Nov 22 10:22:58 PST 2008

On Fri, Nov 21, 2008 at 5:50 PM, Hans J. Koch <hjk at linutronix.de> wrote:
> Hi,
> I used to have a working system with a Radeon X300 (RV370) card and two
> monitors 1680x1050 each. I used an ancient xorg version (something like
> 6.8, can't recall) and had a MergedFB+Xinerama configuration. Worked well
> for me.
> A few days ago I dist-upgraded my Debian sid which brought me version
> 7.3 of xserver-xorg. Since that I'm trying to get my dual head setup
> working again...
> I understand that MergedFB has been replaced by RandR 1.2 extensions.
> Sounds like a good concept to me, but unfortunately it doesn't work here.
> X correctly detects my hardware, but no matter what I do, I always have
> the same output on DVI-0 and VGA-0. I googled around and found a lot of
> pages describing how to setup xorg.conf, and I think it's OK.
> Question: Is this supposed to work or a known problem? What do I have
> to do to get a working dual head setup again?

yes it should work.  you may need to add a virtual line to your config
to reserve enough framebuffer space for your config.  This page gives
a pretty good overview of how to configure things with xrandr:

One problem that comes up from time to time is that the xserver will
clone the outputs (drive both monitors with the same display
controller rather than with independent display controllers).  The
xrandr utility doesn't seem to be smart enough to grab a new crtc when
you select multi-head, so you sometimes have to specify the crtc.  run
xrandr --verbose to see how the topology is configured.

You can use this set of commands to specify a crtc:
xrandr --output VGA-0 --off
xrandr --output VGA-0 --crtc1 --mode 1680x1050
xrandr --output VGA-0 --right-of DVI-0


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