As explained in the aforelinked article, for moving towards atomic/nuclear mode-setting, all hardware planes need to be exposed in a consistent interface from the different graphics drivers. These patches spearheaded by Intel unify the plane support into a consistent and standardized interface. See that article plus the forum comments for more details about this ongoing work.
This work was pulled from Rob Clark's branch into the drm-next code by David Airlie. Besides Rob Clark's involvement at Red Hat, there's several Intel open-source developers that have been working on this code. The universal plane support with its user-space interface for Linux 3.15 will be hidden behind a drm.universal_planes module parameter and disabled by default until additional testing has happened.