https://bugs.freedesktop.org/show_bug.cgi?id=39696
--- Comment #4 from Michel Dänzer michel@daenzer.net 2011-08-09 06:39:31 PDT --- (In reply to comment #3)
and with synchronized vertical retrace?
There's no mechanism for that yet in general. However, if you manage to use the same mode for both displays, you might be able to source both of them off the same CRTC, in which case they should be perfectly synchronized.
Can this be set using xrandr or something else?
Yeah, using the --crtc option. With xrandr --verbose you can see which CRTCs an output can use.
2.) Is there a way to switch 3D and video application sync from the internal to the external vsync rate?
There's no such mechanism for 3D yet.
From the user's point of view, xvattr would be expected to set both?
Not sure how xvattr could be expected to affect anything but XVideo.
Some random ideas: All other things being equal, the driver could synchronize to the CRTC of the primary output, which can be changed using xrandr --primary. Or if that's not good enough, we could add special RandR properties for this.