Matrox G550, dual head, 1680x1050

Hans-Jürgen Koch hjk at
Sun Mar 4 13:47:21 PST 2007

Am Freitag, 2. März 2007 16:24 schrieb Tilman Sauerbeck:
> 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.

Meanwhile, I managed to get 1680x1050 to work with matroxfb. Here's proof that 
both monitors really work:

The left monitor is the primary head (/dev/fb0) and shows text on a VT. There 
I issued a command "fbi -d /dev/fb1 image.jpg" that shows a JPEG image on the 
second monitor. Note that there is no X running (The black-on-white text is 
due to a small patch I usually apply to vt.c).

> > * 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.

Meanwhile I doubt this explanation. Here's what fbset has to say:

$ fbset -fb /dev/fb1 --show

mode "1680x1050-60"
    # D: 135.501 MHz, H: 65.396 kHz, V: 59.997 Hz
    geometry 1680 1050 1680 1050 32
    timings 7380 32 224 32 4 136 4
    rgba 8/16,8/8,8/0,8/24

So, even fbset thinks it's 1680x1050. But where does the distortion come 

> I'm curious, can you describe the distortion in more detail/take a
> photo?

Yes, now I've got one:

This shows a KDE login screen. Note that KDE scaled the background image with 
the Debian logo to cover both screens. The right screen is distorted, 
but "working": If I move a window over to the second screen, I see changes 


@matroxfb developers: Thanks a lot, guys! Well done! Most people I asked about 
having a dual-head framebuffer console at 1680x1050 thought it would be 

@mga xorg developers: Well... Can you tell me why the kernel guys can 
initialize and use the second head and you can't? If you can give me hints 
where in the source I can start to look for the bug, I'm willing to spend 
some time there. Is there something I could try in my configuration?

Any hints?


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