It Looks Like HDMI FreeSync/VRR For Linux + Wayland Support Will Eventually Come For AMD
Harry Wentland, a longtime member of the AMD driver team and patch wrangler around the DC display code, was the presenter at XDC2019. One of the big complaints of the AMD FreeSync/Adaptive-Sync Linux support to date has been the lack of supporting HDMI outputs... Wentland explained that on Windows, AMD uses a proprietary AMD-developed protocol for enabling FreeSync on HDMI. Obviously that won't fly for the open-source AMDGPU kernel driver. But as for the formal HDMI Variable Rate Refresh (VRR) support, they note it's "pending" but held up by a HDMI VRR conformance test suite being released. So hopefully once that CTS is available, HDMI VRR will be flipped on for Linux users wishing to enjoy Adaptive-Sync/VRR functionality for HDMI displays.
On the user-space side, RadeonSI OpenGL, Orace (proprietary AMDGPU-PRO driver) OpenGL support, and RADV Vulkan driver support. No comments were made on whether they intend to support FreeSync/VRR with their open-source AMDVLK Vulkan driver.
The other notable limitation to the AMD variable rate refresh support right now is that it's only supported on X11/X.Org desktops. There isn't VRR Wayland support at this time but it was mentioned among the "next steps" with possible VRR support for Wayland's Weston / KDE Plasma / GNOME Shell and even potentially ChromeOS. Other next steps include working on FreeSync support for Linux video playback, other power savings possibilities, and potentially exposing a more explicit interface for enabling other future use-cases around the technology.
Those curious about more details on the current AMD FreeSync Linux support can see the PDF slide deck from XDC2019.
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