This is helpful to tell which path is taken: 1. explicit modifier: legacy_scanout=0, prime_blit=0 2. prime blit: legacy_scanout=0, prime_blit=1 3. legacy scanout: legacy_scanout=1, prime_blit=0 To be noted, venus doesn't advertise legacy scanout support, but we implicitly support it for gamescope compatibility. Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/38457>