This work came out of a discussion at the Display Next hackfest in Toronto, see https://hwentland.github.io/work/2025hackfest-notes.html#scheduling-atomic-commits .
In contrast to David's suggestion in the last paragraph there, I went for a separate property for the deadline, mainly for these reasons: 1. Communicating the deadline via events would require sending one event per CRTC, which I'd rather avoid due to the experience with page flip events. 2. I'm assuming the property value doesn't need to change between modesets. If this turns out to be wrong for some hardware, may need to reconsider. libdrm MR: https://gitlab.freedesktop.org/mesa/libdrm/-/merge_requests/426 mutter MR: https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/4540
