Enabling AMD Radeon FreeSync On Linux 5.0

[Masush5]

What exactly does this mean? I assume freesync is still working on the driver level but you won't see any benefits since the compositors don't support it? I.e. you'd still be at fixed refresh rates when on your desktop?

What good would freesync actually do for a desktop compositor? They can just sync with the monitors max refresh rate (aka vsync), no need for variable refresh rate.

[Guest]

One thing to note is that AMD and NVIDIA have only added support for Adaptive Sync that's part of the DisplayPort specification - so only GPUs that support Freesync, AMDGPU DC and have a DisplayPort port, can be used with a DisplayPort cable, with a display that supports Freesync, and which has DisplayPort input port, and all of these must support the relevant DisplayPort standard.

AFAICT Freesync over HDMI hasn't been implemented, and might not ever be (since it means Intel and NVIDIA can see how it works and implement support in their own drivers assuming the hardware supports it).

It's stupid that this is only supported on X so far - I guess support must be added by various Wayland compositors, and then it can be used. Since applications already commit buffer changes atomically, I don't think we need any extra Wayland protocol on the application side, except maybe for XWayland applications.

[schmidtbag]

Freesync over HDMI is not supported at the moment. However some code for the HDMI support exists in the amdgpu kernel driver. Displayport has much higher priority for the amdgpu Linux support. I sold my HDMI only freesync monitor because of this. I made a bug report and nothing happened in a month.

Is that a limitation due to the GPU drivers or the protocol? Because if it's the former, couldn't a DP-to-HDMI adapter work?

[davidbepo]

Freesync over HDMI is not supported at the moment. However some code for the HDMI support exists in the amdgpu kernel driver. Displayport has much higher priority for the amdgpu Linux support. I sold my HDMI only freesync monitor because of this. I made a bug report and nothing happened in a month.

link to the bug report?

[Brisse]

In case you (or somebody on this forum) own a 144Hz monitor: Is FreeSync of 40-144Hz beneficial over plain 144Hz refresh rate? Does FreeSync result in less stuttering compared to plain 144Hz assuming the game is rendering frames at 40-80 FPS?

Yes, yes and yes

Freesync actually works much better with a high refresh rate monitor than a 60hz monitor because the latter always has much too narrow frequency span and it's not possible to do low framerate compensation (LFC) with such narrow range.

A 40-60hz monitor can only synchronize between 40 and 60fps.
A 40-144hz monitor can synchronize perfectly from about 13fps to 144fps thanks to LFC.

Not sure if LFC is implemented in Linux yet though.

[Brisse]

What good would freesync actually do for a desktop compositor? They can just sync with the monitors max refresh rate (aka vsync), no need for variable refresh rate.

Actually, it can be detrimental to the desktop experience. As an early Freesync adopter I got to experience that first hand on Windows where in the early days it was buggy and sometimes messed up the desktop experience and video playback. No video player except the default in Windows could handle variable refresh properly and they would become confused and refresh rate fluctuated all over the place with very stuttery video playback as a result.

[shmerl]

Did anyone test it in KDE Wayland session?

[perpetually high]

Does anyone know if I can leave TearFree on in addition to the VariableRefresh setting in the conf? Will that prevent FreeSync from working?

[DarkFoss]

My old Samsung S23A950D died I replaced it with an Acer ED242QR A . Nm figured it out
I've just been setting freesync temporarily with

DISPLAY=:0 xrandr --output DisplayPort-0 --set "freesync" 1

Got it from an AMD support page

[M@yeulC]

What good would freesync actually do for a desktop compositor? They can just sync with the monitors max refresh rate (aka vsync), no need for variable refresh rate.

I can see a couple of benefits: sync to the lowest supported refresh rate when nothing moves, in order to save energy, and enable freesync for windowed applications (though it gets more complicated with more apps, as you have to find a common denominator).
Imagine smooth video playback in windowed mode, for instance (and no, 60FPS doesn't cut it --unless that's what your video is using that framerate--, your video player has to choose between adding interpolated frames, or add some jitter to the output).

I mostly use wayland compositor these days (sway, plasma is almost there besides a few quirks and crashes), so I hope it'll come there as well eventually. Then I might invest in a new monitor