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HDR Colors De-saturated with DisplayPort (Alienware AW3423DWF)

Brief summary of the problem:

Enabling HDR mode in KDE Plasma 6 beta 2 results in very de-saturated colors on my Alienware AW3423DWF monitor when connected via DisplayPort. When I set the "SDR Color Intensity" setting in KDE Plasma to 100% (this "stretches" SDR sRGB content to rec2020), I get fairly accurate sRGB colors. It looks like rec.2020 color vales are handled as rec.709. Apart from the seemingly wrong colorspace, HDR seems to work fine.

Connecting the same Monitor via HDMI instead, results in correctly handled colors. In both cases, connected with HDMI and DP, the connector colorspace is set to BT2020_RGB according to drm_info

On Linux YCbCr is used (according to the monitor OSD) when the monitor is connected via HDMI and RGB when connected via DisplayPort. I checked the behavior of the same hardware on Windows 10 where the correct colorspace is used on DP connections with RGB and YCbCr formats. The monitor also handles the colors correctly on macOS with both HDMI and DP.

Initially reported as KWin bug here

Hardware description:

  • CPU: AMD Ryzen 9 5900X
  • GPU: Radeon RX 7900 XTX (Advanced Micro Devices, Inc. [AMD/ATI] Navi 31 [Radeon RX 7900 XT/7900 XTX] [1002:744c] (rev c8))
  • System Memory: 64 GB of DDR4
  • Display(s): Dell Alienware AW3423DWF (Firmware: M3B104; reproducible in all HDR modes)
  • Type of Display Connection: DP

System information:

  • Distro name and Version: Fedora 40 (rawhide)
  • Kernel version: 6.7.0-0.rc7.20231229git8735c7c84d1b.58.fc40.x86_64 (also tested 6.6.8-200.fc39)
  • Custom kernel: no
  • AMD official driver version: N/A (using mesa 23.3.1-4.fc40)
  • Session: Wayland KDE Plasma 6 beta 2

How to reproduce the issue:

  • Connect the Monitor via DP
  • Enable HDR
    • Outcome: colors are desaturated
    • Expected: SDR content should be shown as sRGB
  • Increase "SDR Color Intensity" to 100% (default was 0%)
    • Outcome: SDR content looks correct (sRGB)
    • Expected: SDR content is oversaturated (filling rec.2020)
  • Switch the connection to HDMI and enable HDR again
  • Outcome: SDR content is handled as expected (sRGB per default; completely oversaturated with maxed out "SDR Color Intensity")

Attached files:

Log files

Kernel log (Monitor connector switches are annotated with # NOTE:): kernel.log