Bug 512959

SUMMARY
Disabling KDE Plasma HDR on this OLED laptop when running in Hybrid GPU Mode causes a complete failure in display control. The screen brightness becomes permanently stuck at an uncontrollably high level. Furthermore, the display rendering is grossly incorrect. Light areas are blindingly intense, while dark areas are too dark, making the image look distorted and unusable. The system's brightness slider has zero effect. This critical issue only occurs in Hybrid GPU mode; using dGPU or iGPU-only modes (selecting it from the BIOS) works correctly after HDR is disabled.

STEPS TO REPRODUCE
1. Ensure the laptop is running in the Hybrid GPU Mode (using both Intel iGPU and Nvidia dGPU).
2. Enable KDE Plasma HDR.
3. Calibrate the HDR settings.
4. Use the system with HDR enabled (brightness control works correctly here).
5. Disable KDE Plasma HDR.

OBSERVED RESULT
After disabling HDR in Hybrid GPU Mode:
- The screen brightness immediately jumps to an uncomfortably high level.
- The overall display appearance becomes visually distorted: lighter parts are extremely bright, and darker parts appear too dim.
- The brightness slider in KDE has no effect on the screen brightness.

EXPECTED RESULT
After disabling HDR, the display should revert to standard SDR mode with:
- Controllable brightness via the system slider.
- Correct visual appearance and gamma.

SOFTWARE/OS VERSIONS
Operating System: CachyOS Linux
KDE Plasma Version: 6.5.3
KDE Frameworks Version: 6.20.0
Qt Version: 6.10.1
Kernel Version: 6.18.0-rc7-1-cachyos-rc-lto (64-bit) | (Tried other available kernels, but they had the same issue.)
Graphics Platform: Wayland
Processors: 28 × Intel® Core™ i7-14700HX
Memory: 32 GiB of RAM (31.1 GiB usable)
Graphics Processor 1: Intel® Graphics
Graphics Processor 2: NVIDIA GeForce RTX 5060 Laptop GPU
Manufacturer: LENOVO
Product Name: 83LY
System Version: Legion 5 15IRX10

ADDITIONAL INFORMATION
- The issue is specifically triggered by the HDR workflow: Standard SDR functionality was perfect before HDR was first enabled and calibrated on the system. The inability to return to controllable SDR mode only began after enabling, calibrating, and then disabling KDE Plasma HDR.
- Re-enabling HDR immediately restores brightness control and corrects the display output. Disabling HDR again causes the issue again.
- The issue does not occur when the laptop is switched to dGPU mode or iGPU-only mode via the BIOS. In these modes, disabling HDR works correctly.
- The issue occurred on multiple operating systems, including CachyOS and OpenSUSE Tumbleweed.
- A different kernel (linux-cachyos-lts) which failed to recognize the dGPU did not exhibit the issue (effectively acting as iGPU-only mode), further pointing to the hybrid setup being the root cause.

Attempts to Fix (All Failed)
The following troubleshooting steps were attempted without success in resolving the issue or restoring proper SDR functionality:
- Rebooting the system.
- Recalibrating HDR multiple times.
- Creating a new user profile.
- Switching the display protocol from Wayland to X11.
- Reinstalling all packages.
- Switching between various kernels.
- Attempting a "clean" disable: Switching the BIOS to dGPU or iGPU-only mode (where SDR works correctly), ensuring HDR was disabled, reinstalling all packages, rebooting, and then switching the BIOS back to Hybrid Mode. The issue immediately returned upon re-entering Hybrid Mode.