DisplayPort 2.1 support

Hi there!

So I got the brand new Samsung Odyssey neo G9 (57") which is the first monitor to use DisplayPort 2.1 as it is basically a dual UHD (7680 x 2160) @240hz but I had to switch the monitor to DisplayPort 1.4 to get it working on my Manjaro.

Its not that bad as the monitor works at full res but half the refresh rate: 120hz. The thing that is botherring is that I have to go to my monitor settings to set DP to 1.4 everytime I want to boot my Manjaro.

I am using the open source AMD driver and kernel 6.5.0-1-MANJARO.
Graphics card: 7900 XTX

Any idea on how to solve this?

Note that I did not try the proprietary AMD driver.


Hello @maraud :wink:

Well when I investigate the specifications, then one DP2.1 cable can only 4k@240hz. If that are 2 screens , so 2 lanes, then it would half of it. At least the hertz are here halved, because of the max bandwidth. Probably DSC (compression) can help, but no idea if Linux supports it here. If it works on Windows, then you can assume that it is because of DSC.

Your screen has also 2 hdmi inputs. I would suggest using these inputs instead. :man_shrugging:

It is a 32:9 screen with a 7680 x 2160 resolution. It is within DP2.1 specs, it works well on windows! Not sure if it needs DSC at all.

@maraud Look here is a good table: DisplayPort - Wikipedia

UHBR 20 supports max. 77.37 Gbit/s

2x4k@240hz → 2x68.56 Gbit/s will not work without DSC, that’s for sure here, but even with compression: 2x54.84 Gbit/s I doubt that you get full 240hz on Windows, maybe has a good technique to lower it maybe to fit the max rate or better compression. No idea.

Maybe check the journal. There must be hint when DSC is working.

At least DSC is there on the kernel, but I don’t know its limits or how far the implementation goes: https://github.com/torvalds/linux/tree/e017769f4ce20dc0d3fa3220d4d359dcc4431274/drivers/gpu/drm/amd/display/dc/dsc

Even on HDMI2.1 4k@240hz is only possible with DSC due the bandwidth limit. HDMI - Wikipedia Possibly Linux has support for DSC on HDMI for each cable. :man_shrugging: