Well at least here on nvidia-755m if nvidia_drm modeset is enabled gdm3 fails to boot. However lightdm works fine & prime sync is enabled..
$ sudo cat /sys/module/nvidia_drm/parameters/modeset [sudo] password for doug: Y doug@doug-Lenovo-IdeaPad-Y510P:~$ xrandr --verbose Screen 0: minimum 8 x 8, current 1920 x 1080, maximum 16384 x 16384 eDP-1-1 connected primary 1920x1080+0+0 (0x46) normal (normal left inverted right x axis y axis) 345mm x 194mm Identifier: 0x42 Timestamp: 11726 Subpixel: unknown Gamma: 1.0:1.0:1.0 Brightness: 1.0 Clones: CRTC: 0 CRTCs: 0 1 2 Transform: 1.000000 0.000000 0.000000 0.000000 1.000000 0.000000 0.000000 0.000000 1.000000 filter: EDID: 00ffffffffffff0030e4d90200000000 00150103802313780a15d59e59509826 0e505400000001010101010101010101 0101010101017e3680b070381f403020 350059c2100000190000000000000000 00000000000000000000000000fe004c 4720446973706c61790a2020000000fe 004c503135365746312d544c4232004b PRIME Synchronization: 1 supported: 0, 1 -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1752739 Title: PRIME Synchronization doesn't work with linux-kernel 4.15. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/nvidia-graphics-drivers-390/+bug/1752739/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs