radeon driver and dual head

Alex Deucher alexdeucher at gmail.com
Tue Aug 5 12:31:34 PDT 2008

On Tue, Aug 5, 2008 at 12:49 PM, Jethro Tull <heavytull at hotmail.com> wrote:
> I'm trying to setup the dual head on my laptop.
> i'm running Xorg 7.3/Slackware12.1
> I connected an old monitor at the VGA plug.
> the monitor can do up to 1024x768px² in resolution.
> but when i type xrandr -q i get the following:
> ~$ xrandr -q
> Screen 0: minimum 320 x 200, current 1280 x 800, maximum 1280 x 1200
> VGA-0 connected 640x480+0+0 (normal left inverted right x axis y axis) 260mm
> x 195mm
>    640x480        60.0*
> LVDS connected 1280x800+0+0 (normal left inverted right x axis y axis) 0mm x
> 0mm
>    1280x800       60.0*+
>    1024x768       60.0
>    800x600        60.3
>    640x480        59.9
> S-video disconnected (normal left inverted right x axis y axis)
> so it says that only the 640x480px² mode can be on.
> i tried:
> #xrandr --output VGA-0 --mode 1024x768
> xrandr: cannot find mode 1024x768

Looks like either your monitor is not providing an edid so the driver
falls back to load detection and you get some server default mode
which is usually 1024x768, but perhaps you are using an old xserver?
Anyway, you can add a new mode using xrandr:

xrandr --addmode VGA-0 1024x768
xrandr --output VGA-0 --mode 1024x768

Those commands will add the 1024x768 mode from the LVDS output to the
VGA output.  If you want to specify a previously undefined mode, use
the following commands:

xrandr --newmode my_mode 63.50  1024 1072 1176 1328  768 771 775 798
-hsync +vsync
xrandr --addmode VGA-0 my_mode
xrandr --output VGA-0 --mode my_mode


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