Backlight control not working on Lenovo IdeaPad Gaming 3 with Renoir / AMDGPU

The brightness (LCD backlight) controls on a Lenovo IdeaPad Gaming 3 (15ARH05, LCD display, AMD Renoir CPU Ryzen 5 4600H, discrete NVIDIA GeForce 1650 Ti Mobile) are not working: - Fn keys show the brightness slider on the display moving. - /sys/class/backlight/amdgpu_bl0/brightness changes accordingly from 0 to 255. - The display does not show any brightness change. - Manually writing to brightness does not change the display's brightness either. - /sys/class/backlight/amdgpu_bl0/actual_brightness stays at **311**. *I figure **this** indicates a problem with the amdgpu driver.* - The display seems to stay at full brightness always. Adjustments work fine on Windows 10. The laptop is running: - Kali Linux Rolling - linux-image-5.8.0-kali-amd64 (based on 5.8.14) and custom-built kernels 5.9, 5.9.1 and 5.10-rc1, mostly based off the Kali config - X with amdgpu drivers, discrete graphics unused (proprietary NVIDIA drivers loaded and unloaded for testing). I have tried booting with various acpi_backlight kernel options, which lead to various backlights being available in /sys/class/backlight/*/brightness: - acpi_backlight=video: acpi_video0 acpi_video1 amdgpu_bl0 - acpi_backlight=vendor: amdgpu_bl0 ideapad - acpi_backlight=native: amdgpu_bl0 - acpi_backlight=none: amdgpu_bl0 Other things that did not work: - acpi_osi=Linux (no change) - acpi_osi= (hangs at boot) - BIOS update (no other version available) - moving /lib/firmware/amdgpu/renoir_dmcu.bin away - patching [amdgpu_dm.c](https://github.com/Aonnghus/renoir-brightness/blob/master/brightness.patch) I am aware that there has been a number of updates related to backlights for AMDGPUs, like general support and fixes in kernel 5.7.x and updates to the scaling of brightness values >255 in 5.9, but so far this seems not to have helped my case (or possibly, broke more things). I am not looking for: - software alternatives - adjusting the gamma values - using discrete graphics (if it can be avoided) **What else can I do or look into to gain control of the backlight?** I came across [this comment](https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1861925/comments/27) and [this bug report](https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1899626) , which seem to suggest that some kernel fixes may have broken other things. **What would be the best place to report that?**