I'm trying to use xrandr to give me a triple-head setup, using an HD 6870 (Northern Islands), kernel 2.6.38-rc8 and the latest (released) x.org on 64-bit ArchLinux.
I'm using a pair of 1680x1050 monitors through DVI flanking a 1920x1080 DisplayPort monitor. I can use xrandr to stretch a desktop across any two of these monitors. When I try to do it across all three, one of the two DVI monitors will always black out, and then go into power-saving mode. Turning the suspect monitor off and on does nothing. My Xorg.0.log shows nothing out of the ordinary, and dmesg shows nothing unusual either.
Using fglrx does give me the three desktops successfully, but I'd very much like to stop using that software.
Can someone with a similar setup reproduce this issue?