Add explicit synchronization, with timelines

[emersion]

This PR implements explicit synchronization. Unlike previous attempts, it uses a timeline abstraction based on drm_syncobj like Vulkan.

To inter-operate with other APIs (KMS, EGL, linux-explicit-synchronization-v1), the timeline points can be converted from/to sync_file FDs.

Test with: build/examples/explicit-sync -s weston-simple-dmabuf-egl. Use WAYLAND_DEBUG=server to check that fences are exchanged. To test the DMA-BUF sync_file extraction, use weston-simple-egl as test client (requires kernel patch).

TODO:

• Write an example compositor
• Extract sync_file from DMA-BUF when client doesn't support linux-explicit-synchronization-v1
• Add wlr_texture upload synchronization
• Figure out if this API is okay for Vulkan
• Detect support in backends and renderers
• Add support for cached state to linux-explicit-synchronization-v1
• Documentation
• Sanity checks (e.g. in wlr_output_commit)
• Consider ref'counting wlr_render_timeline
• Output cursors let's wait until output layers for this

Previous work:

• [WIP] linux-explicit-synchronization-v1: new protocol implementation #2070
• Groundwork for wp_linux_explicit_synchronization #1685

Future work:

• Multi-GPU support in the DRM backend
• Wayland backend support

[nyorain]

From a first glance, the API should work for Vulkan. But we need some additional guarantees/documentation. How does a renderer know whether implicit or explicit sync is used for a render buffer? Is a single call to signal_timeline enough to inform the renderer that rendering does not have to be finished by the time renderer_end returns? This is important for Vulkan. I would prefer an explicit parameter to renderer_begin or renderer_end to select the sync mode.

[emersion]

Added some documentation.

@jbeich, what's the correct way to grab <linux/dma-buf.h> on FreeBSD? It's this file in drm-kmod: https://github.com/freebsd/drm-kmod/blob/master/linuxkpi/gplv2/include/uapi/linux/dma-buf.h

[jbeich]

@jbeich, what's the correct way to grab <linux/dma-buf.h> on FreeBSD? It's this file in drm-kmod: https://github.com/freebsd/drm-kmod/blob/master/linuxkpi/gplv2/include/uapi/linux/dma-buf.h

Until https://reviews.freebsd.org/D23085 or https://github.com/evadot/drm-subtree lands probably making a private copy of uapi headers (a la Mesa) or their contents.

@evadot, may know more.

[jbeich]

See also FreeBSDDesktop/kms-drm#156

[evadot]

@jbeich, what's the correct way to grab <linux/dma-buf.h> on FreeBSD? It's this file in drm-kmod: https://github.com/freebsd/drm-kmod/blob/master/linuxkpi/gplv2/include/uapi/linux/dma-buf.h

Until https://reviews.freebsd.org/D23085 or https://github.com/evadot/drm-subtree lands probably making a private copy of uapi headers (a la Mesa) or their contents.

@evadot, may know more.

Yeah we don't have a good way to provide them for now so having a copy would be easier for us.

[emersion]

wlroots has migrated to gitlab.freedesktop.org. This pull request has been moved to:

https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/3282