X.Org's Modesetting Driver Flips Off Atomic By Default

While atomic mode-setting has been around for several years now and to provide a modern mode-setting interface that can test modes prior to the actual operation and reduce possible flickering during mode-setting events and also being faster, the common xf86-video-modesetting driver has at least temporarily disabled the support by default.

Within the latest X.Org Server 1.21 Git and requested for back-porting to X.Org Server 1.20 is disabling atomic support by default. This stems from a black screen when doing rotation on a different CRTC and other problems along the atomic code-path for this in-tree driver. So by default the generic modesetting driver will use the legacy code-path by default to avoid messing up existing users.

The sad part is that X.Org Server atomic improvements have patches available on the mailing list but without any activity to review and merge them. Plus there hasn't been any effort to actually organize an X.Org Server 1.21 release. From Intel open-source developer Maarten Lankhorst who made the change, "The fixes to make the xserver more atomic have been pending on the mailing list for ages."

X.Org Server 1.21 won't be around for this year's Linux distributions but hopefully something can materialize in time for the likes of Ubuntu 20.04 LTS. X.Org Server development activity has continued to wane as the Wayland support on GNOME, KDE, and other compositors continues to improve as well as the Wayland ecosystem in general.