Bug 495219

Created attachment 175128 [details]
This is the diff between the output of `drm_info` before and after the brightness adjustment. Due to file size limitations, the full output is not included as an attachment.

SUMMARY
HDR Mode Reverts to SDR When Adjusting Brightness via Plasma's Brightness Slider on Acer Monitor

STEPS TO REPRODUCE
1. Enable HDR on [Acer] Monitor:
   - Connect Acer monitor that supports HDR to your system.
   - Set HDR to "auto" in monitor OSD.
   - Open System Settings → Display and Monitor.
   - Enable HDR for the display and apply setting.
2. Adjust Brightness:
   - Use the Plasma brightness slider located in the system tray.
   - Modify the brightness level using either the individual monitor or global brightness slider.

3. Observe HDR Mode:
   - After adjusting the brightness, observe that the monitor switches from HDR to SDR mode.

Note: This issue does not affect my Gigabyte monitor, which allows me to toggle HDR "On" in the monitor OSD which results in it remaining in HDR upon brightness adjustments.

OBSERVED RESULT
- Acer Monitor: Adjusting the brightness via Plasma's brightness slider causes the monitor to switch from HDR to SDR mode. Additionally, after rebooting, turning the monitor off/on, or logging out/in, HDR mode does not persist and reverts to SDR.
- Gigabyte Monitor: Remains in HDR mode consistently, even after adjusting brightness, rebooting, or toggling the monitor's power.

EXPECTED RESULT
Adjusting the brightness via Plasma's brightness slider should modify the display brightness without altering the HDR/SDR mode of the monitor. HDR mode should remain active on the Acer monitor regardless of brightness adjustments, similar to the Gigabyte monitor's behavior.

SOFTWARE/OS VERSIONS
Windows: N/A
macOS: N/A
Linux/KDE Plasma: EndeavourOS (Arch Linux)
KDE Plasma Version: 6.2.1
KDE Frameworks Version: 6.7.0
Qt Version: 6.8.0
Kernel Version: 6.11.4-arch2-1 (64-bit)
Graphics Platform: Wayland
Processors: 20 × 12th Gen Intel® Core™ i7-12700
Memory: 31.1 GiB of RAM
Graphics Processor: AMD Radeon RX 6650 XT

ADDITIONAL INFORMATION
- Monitor Models:
  - Gigabyte Monitor: Gigabyte M27U
  - Acer Monitor: Acer Nitro XV275K P3
  
- Connection Type: DisplayPort 1.4
- Wayland/X11: Wayland

- Clarifications:
  - The issue exclusively affects the Acer monitor, which only allows setting HDR to "Auto" or "Off". In contrast, the Gigabyte monitor allows forcing HDR "On" directly through its settings, avoiding the reversion to SDR when adjusting brightness.

- Related Forum Post:
  - https://discuss.kde.org/t/plasma6-2-super-buggy-hdr-mode/23161

- Video Demonstration:
  - https://youtu.be/iJZ-aviftSQ

- Workarounds Tried:
  - Manually re-enabling HDR after each brightness adjustment. This works, however is inconvenient.