Goal

• Mutter should support direct scanout of wayland buffers on secondary GPUs in multi-GPU systems. Right now mutter only supports direct scanout for buffers which are compatible with the primary GPU. Implementing this will help enable further features and improve performance of fullscreen PRIME apps on discrete GPU laptops.

• • For example: A user is playing a game on a NVIDIA optimus laptop (Intel/AMD integrated GPU + NVIDIA discrete GPU). The game is offloaded to the NVIDIA GPU and is running fullscreen on a display output connected to the NVIDIA GPU. Without this feature the game's frames must be copied to the integrated GPU and then copied back to the NVIDIA GPU, hurting performance.
• This is also a prerequisite to features such as Dynamic Display Muxing, where in order to flip the Display mux to the NVIDIA GPU in a dual-GPU system we first need to be able to scan out buffers on the NVIDIA GPU.

Acceptance Criteria

• Wayland buffers that support direct scanout on secondary GPUs can be scanned out, see example scenario above.

Equivalent work for wlroots: https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/4055