https://bugs.freedesktop.org/show_bug.cgi?id=89155
--- Comment #5 from Adam Reichold adam.reichold@t-online.de --- I had some more time to test this (now on kernel 4.1.4 and X server 1.17.2) and have made two hopefully useful observations:
* The Catalyst driver (version 15.7) is always able to initialize the setup even though VGA-connected monitor seems to always "flicker" two times before reaching the final mode.
* I have found a somewhat reliable workaround to use with the free driver: By adding
xrandr --output VGA-0 --off
before
xrandr \ --output VGA-0 --preferred --primary \ --output DVI-0 --preferred --rotate left --right-of VGA-0
to my .xinitrc, the system will properly initialize both displays even though the first command seems to take around two seconds to complete.