how to ignore monitor's EDID?

Alex Deucher alexdeucher at
Sun Dec 28 09:33:32 PST 2008

On Sun, Dec 28, 2008 at 7:43 AM, Tomasz Chmielewski <mangoo at> wrote:
> I have a radeon 9600 card, with two devices connected:
> - DVI: LCD monitor, capable of 1280x1024 (preferred mode)
> - VGA: LCD projector, capable of 1024x768, (800x600 preferred mode)
> Both devices show the same output ("clone" - of course, if the
> resolution is 1280x1024, VGA/LCD projector does not show any output, as
> this device does not support this mode).
> The problem is - whenever the LCD projector is powered on as computer
> boots, X starts in 800x600 resolution.
> What's worse - it's not possible to change the resolution to 1280x1024;
> xrandr will only switch the resolution up to 1024x768 (maximum supported
> by the VGA monitor).

There are two types of clone modes, one where one crtc drives two
outputs with the same timing (what you are seeing), and one where each
output is drive by a separate crtc.  xrandr is not always smart enough
to do the right thing when you request different timing on two
different outputs if they are currently both being drive by the same
crtc.  the following command should do what you want:
xrandr --output DVI-0 --crtc 1 --mode 1280x1024

> Is it possible to force the resolution on a device, even if it doesn't
> support it?

yes.  that's what the "PreferredMode" option is for.  See this page
for more on randr 1.2 xorg.conf options:

Something like this should do the trick:

Section "Monitor"
    Identifier      "DVI-0"
    DisplaySize     304 228
    Modeline "1280x1024_60.00"  108.88  1280 1360 1496 1712  1024 1025
1028 1060  -HSync +Vsync
    Option "PreferredMode" "1280x1024_60.00"

You can also add a similar section for VGA-0.


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