Matrox G550, dual head, 1680x1050

Tilman Sauerbeck tilman at
Fri Mar 2 07:24:20 PST 2007

Hans-Jürgen Koch [2007-03-02 16:10]:
> Am Freitag 02 März 2007 15:39 schrieb Tilman Sauerbeck:
> > Hans-Jürgen Koch [2007-03-02 10:53]:
> > > I'm the proud owner of two NEC MultiSync 2070WNX monitors (1680x1050) and
> > > a Matrox G550 dual DVI card. I'm now trying to set up a dual head
> > > configuration with this equipment.
> > >
> > > [snip]
> > >
> > > Is this a known limitation of matroxfb? Or a X server bug?
> >
> > AFAIK matroxfb doesn't support the G550 dual DVI card. The mga X driver
> > certainly doesn't support it yet. 
> Well, at the moment I'm using the VGA outputs. Current status is:

I believe/suspect the hardware doesn't care whether you use the 2VGA
cable or the 2DVI cable. Unfortunately, I only have the dual-dvi cable
so I cannot be sure. Last time I had a close look at dual-dvi was around
christmas and I don't remember all the details ;)

> * 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

> * 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?

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.


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