Problem setting up dualhead with notebook and xrandr

[Alex Deucher]

On Wed, Jan 28, 2009 at 4:24 AM,  <kzot at gmx.net> wrote:
> 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.

randr may not deal well with having all outputs disabled.  try:
xrandr --output DVI-0 --off
xrandr --output LVDS --crtc 0 --mode 1400x1050
xrandr --output VGA-0 --off

Alex