Bug#495267: Upstream commit which causes this

[Alex Deucher]

On Fri, Aug 22, 2008 at 3:19 PM, Jed Davis <jld at ccs.neu.edu> wrote:
> On Sat, Aug 16, 2008 at 02:20:52PM +0200, Michel Dänzer wrote:
>> On Sat, 2008-08-16 at 13:05 +0200, Florian Weimer wrote:
>> > * Michel Dänzer:
>> > >
>> > > I suspect this is a case of the xrandr utility not being smart enough to
>> > > automatically select different CRTCs for the outputs. Try choosing them
>> > > explicitly with --crtc.
>> >
>> > Doesn't seem to work, either.  If I use --crtc, one of the screens just
>> > stays dark.
>>
>> Please provide the exact command line you tried and the output of xrandr
>> --verbose afterwards.
>
> I'm having a similar problem, and I've attached a transcript of trying
> to change the CRTC.  The transcript starts out with the monitors cloned
> and refusing to un-clone; the "xrandr --output DVI-0 --crtc 1" causes
> that monitor to go blank; and the "xrandr --output DVI-0 --crtc 0"
> restores the original problem.

I guess you'll have to specify a mode as well since just --crtc seems
to disable the output.  Try:
xrandr --output DVI-0 --off
xrandr --output DVI-0 --crtc 1 --mode 1024x768

Alex