Can't use 165hz monitor with 10bit HDR on KDE Plasma 6

Graphics / Linux Linux
1

Hello,

I recently made the switch from Windows to Linux (Nobara - KDE Plasma 6 with Wayland) and have been having trouble getting HDR to work on my AW3423DWF monitor. Technically this monitor is advertised as being able to run at 165hz with HDR at 3440x1440 however that is only with 8bit HDR not 10bit. At 10bit HDR, the monitor’s refresh rate is set to its next lowest mode which is unfortunately 100hz.

I did not experience this issue on Windows because Windows will automatically lower the HDR to 8bit with dithering which is supported by the monitor. There does seem to be workarounds to get 144hz or 165hz with 10bit HDR (see here) however all of these workarounds are Windows specific.

The new and experimental HDR support for KDE plasma 6 seems to be 10bit to my knowledge as I am unable to set my refresh rate to 165hz and am instead limited to 100hz. When I disable HDR I am able to get to 165hz. This is pretty disappointing to me and I’m wondering if anyone has a solution that either:

  1. Involves a Linux specific workaround similar to the Windows where I am able to get the monitor to 144hz or 165hz with 10bit HDR

  2. Downgrades the HDR on my OS to 8bit or 8bit + dithering so that I can make use of the full 165hz refresh rate

  3. Does some clever trick that I haven’t thought of

My PC specs in case they matter:
Distro: Nobara 40 - NVIDIA
GPU: RTX 4090
CPU: Ryzen 9 5900X
RAM: 32GB
Motherboard: rog strix gaming wifi ii
Cable: Display Cable 1.4

Thanks in advance!

2

I think that if you use kscreendoctor you can enable HDR without wide color gamut using this command:

kscreen-doctor output.DP-1.hdr.enable

Change “DP-1” to your monitor output, you can check it with this other command:

xrandr --listmonitors

To also enable wide color gamut you can use this, but I think it will limit your monitor to 100Hz:

kscreen-doctor output.DP-1.wcg.enable

Each command can be disabled changing the “enable” part at the end with “disable”.

You can assign them to keyboard shortcuts in Plasma settings to enable/disable HDR more conveniently if it works for you.

3

You can use CRU on Windows, then export the EDID in txt format and load it in Linux. It’s easy with X11, but since you’re using Wayland it’s a bit more complicated and apparently it disables VRR:

https://forums.developer.nvidia.com/t/custom-edid-in-wayland/302923