One of the few features not yet provided by the mainline open-source Radeon Linux graphics driver will soon be crossed off the list… FreeSync / Adaptive-Sync / HDMI Variable Refresh Rate support.
It’s been a heck of a long time coming to say the least, but last month AMD began posting new patches for VRR / Adaptive-Sync / FreeSync for their open-source Linux graphics driver. Part of the reason why it’s taken so long getting to this point was reaching a consensus with the Intel Linux graphics driver developers and other Linux DRM stakeholders over the design/properties to use in exposing this functionality to user-space so eventually other Linux graphics drivers can choose to implement this support similarly.
For those well behind on your technology reading and Phoronix articles, Adaptive-Sync and HDMI VRR are the industry standards for variable refresh rates to reduce (or ideally, avoid) stuttering, tearing, and input lag primarily for gaming.
Sent out a short time ago were the latest Linux DRM and Mesa patches for plumbing in the infrastructure for handling this capability. This marks the fourth revision to this patch series for what will hopefully soon be mainlined.
This includes the DRM API for what gets exposed to the user-space for enabling VRR support. This latest update includes some documentation/formatting updates and minor changes in the AMDGPU display code.
There are also the updated Mesa patches. The newest Mesa patches update the blacklist of desktop environments to avoid applying this behavior to the desktops. There is also a fix in these patches with the variable refresh property handling.
That blacklist covers desktops like KWin, Compton, Compiz, Muffin, and others from using adaptive synchronization as well as programs like Chrome, Firefox, Totem, VLC, and other browsers and common desktop applications.
It does look like this code is just about over the finish line. Unfortunately, it seems too late for including the DRM bits in the upcoming Linux 4.20~5.0 kernel so it will have to wait until after that for merging. But at least it looks like the first Linux kernel release of 2019 could include this support! That would also pair with Mesa 19.0 or so for making this long-awaited feature a reality for open-source AMD Linux gamers. Tests, setup guides, and more to come once all of this code has been merged.
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