Matrox G550, dual head, 1680x1050

Hans-Jürgen Koch hjk at
Fri Mar 2 07:59:34 PST 2007

Am Freitag 02 März 2007 16:24 schrieb Tilman Sauerbeck:

> > * Without X (boot, VT) I get clean 1280x1024 on both monitors. The
> > monitors interpolate that to their native resolution, both show the same
> > image.
> Hrrrm, I don't think the second monitor gets a signal with my G550 +
> dual-dvi cable.
> > * With a xinerama configuration, X starts without any (EE) errors.
> > Monitor1 shows a clean 1680x1050 image, Monitor2 a distorted image. I can
> > move the mouse or windows from one monitor to the other. The reason for
> > the distortion on monitor2 is most probably that the card is still
> > configured for 1280x1024 while the X server thinks it's 1680x1050.
> I'm curious, can you describe the distortion in more detail/take a
> photo?

It looks like about 10 parallel stripes that are not horizontal, but with a 
slight slope downwards (from left to right). I'll take a photo and put it on 
the web, but it'll take some time, I can't do that right now.

BTW, I just tested this xinerama configuration with both screens forced to 
1280x1024, and that works! It doesn't look good, though. So this proves that 
the open source drivers handle everything properly, they just fail to 
initialize the second channel correctly if you have a non-VESA resolution.  

> > * With a mergedfb configuration, X starts with this error:
> > (EE) MGA(0): HALLib not loaded! NOT using "Merged Framebuffer" mode.
> > Afterwards I have the same image on both monitors, both clean and in
> > 1680x1050.
> There's a huge difference between real "dual head" and clone mode.
> For clone mode, you just need to set up the second output correctly, and
> tell it to get its data from the first CRTC.
> If you want an indepedent second display, you need to set up the 2nd
> CRTC, too.
> > For me, this doesn't look like "not supported". Obviously, there is a
> > (small?) bug that prevents the second screen from setting the mode
> > correctly in some configurations (xinerama). But both monitors can
> > definetly output a clean 1680x1050 image using this version of
> > xserver-xorg.
> Could you test whether you get the exact same behaviour (for the
> different situations you described) if you use the dual-dvi cable and
> to connect your monitors?

Unfortunately, I don't have the dual-dvi cable (yet). I really like to see 
this working with VGA cables before I spend 49 Euros for that cable.

> I plan to implement support for the G550 dual DVI this year, but haven't
> figured it out completely yet. It would help to know whether the cable
> type used matters or not.
> > > You could use Matrox' official drivers
> > > though.
> >
> > These are closed source, aren't they?
> They consist of a slightly modified version of xf86-video-mga and the
> proprietary mga_hal/hallib module.

I'd like to avoid that.


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