MergedFB and multiple external monitors

Alex Deucher alexdeucher at
Wed Jan 3 06:14:10 PST 2007

On 1/3/07, Martin Langhoff <martin.langhoff at> wrote:
> [I'm not on the list, please CC ;-) ]
> Hi again, and sorry for spamming the list with a string of issues, all
> together and in one go. Happy to RTFM where relevant, and invite a
> good cold beer in the next Conf we meet ;-)
> MergedFB rocks for a laptop user like me with an external DVI port to
> hook up to just about anything. However, it currently depents [at
> least for me] on starting hooked up to a monitor, and from that
> point onwards, I can use xrandr to switch the modes that are valid
> from that monitor.
> Which is kind of uncomfortable. Is it possible to define a few
> modelines such as the modelines for my work and home LCDs, and then a
> few standard monitor settings like 1024x768 and 800x600 to be able to
> hook up to arbitrary projectors and random monitors?
> [I _may_ have found a way do do this, actually. Initially, I could not
> get to pay attention to the 2nd monitor definition, because I
> had listed it in a 2nd "screen" section, that would only be used if I
> was doing Xinerama. My workaround is to list 2 monitors in the main
> Screen section and there I can set a modeline. I now have to test with
> a few more modelines to see if I can force it even if the monitor is
> not hooked in.]
> And in that case... are there safe "baseline" modelines that I can use
> without risk of blowing up the gear I connect to ;-) ?

Take a look at the radeon man page.  You can force mergedfb on and
define hsync and vrefresh ranges for crtc2, then just define metamodes
with the configurations you want.


> cheers,
> martin

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