Hello. I can confirm this behavior on an IBM ThinkPad T42 with Radeon graphics.
martin@shambhala:~> lspci -nn | grep VGA 01:00.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc. [AMD/ ATI] RV350/M10 / RV360/M11 [Mobility Radeon 9600 (PRO) / 9700] [1002:4e50] For me it appears to be related to Flickering ATI X1300 r300 Mesa 17.2 https://github.com/sddm/sddm/issues/898 However disabling vsync for r300 driver did not help. I tried it via .drirc in /root and in /var/lib/sddm like this: <driconf> <device screen="0" driver="r300"> <application name="Default"> <option name="vblank_mode" value="0" /> </application> </device> </driconf> I also tried "dri2" as driver name. Thanks, -- Martin