NVIDIA Contributes linux_dmabuf v4 Feedback Support To XWayland

NVIDIA engineer Austin Shafer has contributed linux_dmabuf v4 feedback protocol support for upstream XWayland. This is working towards allowing scan-out modifiers that a compositor advertises to be delivered to X11 applications under (X)Wayland.

At the end of 2021 the Wayland DMA-BUF feedback extension was introduced and now thanks to the work of NVIDIA this is wired up for XWayland. The "feedback" addition to the Linux DMA-BUF protocol is particularly useful for modern multi-GPU setups where needing to know about the GPU device in use by the compositor and the semantics around it such as if using the secondary GPU that DMA-BUF can still exchange buffers with the main GPU and in a compatible format.

In the time since this DMA-BUF feedback extension was added to Mesa and wired up elsewhere. The X.Org code meanwhile over the course of last year saw updates by Austin Shafer for DRI3 additions to let a client tell the server what DRM device is being used, so that the X.Org Server can make more informed decisions for what modifiers to return to the client. With those prerequisites out of the way, the XWayland support for linux_dmabuf v4 feedback was finally merged on Friday.

More details for those interested via this X.Org Server MR that will now be found in the next release of XWayland.