Problem setting up dualhead with notebook and xrandr

[kzot at gmx.net]

On Wednesday 07 January 2009 17:51:35 Alex Deucher wrote:
> On Wed, Jan 7, 2009 at 5:35 AM,  <kzot at gmx.net> wrote:
> > Setup is as follows: T60 Notebook in docking station (display "LVDS" and
> > resolution 1400x1050) and two external displays via DVI (display "DVI-0"
> > and resolution 1280x1024) and VGA (display "VGA-0" and resolution
> > 1280x1024).
> >
> > Goal is to disable the notebook display and have a dualhead on the two
> > external displays.
> >
> > I disabled the LVDS display via "xrandr --output LVDS --off" and tried to
> > enable the external displays in dualhead mode "xrandr --output VGA-0
> > --left-of DVI-0". Which does not change anything.
> >
> > What can be wrong here?
>
> Both outputs are being driven by the same crtc (controls display
> timing and fb offset).  This allows you to drive all three monitors at
> the same time (LVDS on one crtc, DVI/VGA on the other).  To run them
> on separate crtcs, specify the crtc with randr.  run xrandr --verbose
> to see the crtc assignments.
> xrandr --output LVDS --off
> xrandr --output VGA-0 --crtc 0 --mode 1280x1024
> xrandr --output DVI-0 --crtc 1 --mode 1280x1024

Thanks this did the trick - for one time. With

xrandr --output LVDS --off && \
xrandr --output DVI-0 --crtc 0 --mode 1280x1024 && \
xrandr --output VGA-0 --crtc 1 --mode 1280x1024 && \
xrandr --output DVI-0 --left-of VGA-0

I was able to have a dualhead setup with the two external display. When 
switching to the notebook display alone with

xrandr --output DVI-0 --off && \
xrandr --output VGA-0 --off && \
xrandr --output LVDS --crtc 0 --mode 1400x1050

the command chain for dualhead set-up results in a buggy set-up. The VGA-0 
display remains dark; I can move the mouse over it and see it but when I try 
to move windows over there they are not displayed. The output "xrandr --
verbose" of the first dualhead and the second dualhead set-up are absolute the 
same.

Any hints?