Laptop Brightness Controls not working

On my Clevo P770ZM laptop, which officially supports Nvidia 900M series discrete GPUs, I have got an AMD R9 M290X graphics card installed. The card is detected as AMD HD 8970M by the OS (Win 8.1 Pro x64) and the display brightness controls don’t work. This system does not have any kind of hybrid or switchable graphics. All display ports are directly wired to the dGPU and Intel iGPU is internally disabled in the system. So, the AMD GPU directly interfaces with the laptop display (which is LP173WF4 SPD1).

The system BIOS normally reports what GPU is installed, but in my case it can’t identify the AMD GPU. However, besides the brightness issue, the system works fine (except for some microjitter in games).

I have tried updating the BIOS and using different GPU driver versions from very old to the latest, but could not make the brightness controls work. Windows brightness controls, that are accessible through Charms Bar -> Settings, are greyed out. Clevo Hotkey Utility crashes every time I open it. Does anyone here know of any way to make the brightness controls work on this AMD system?

I have tried several third party display brightness control software too. Either they don’t work or they just reduce the brightness through software but not reduce the backlight. The laptop display runs at its highest backlight setting, which is too bright for indoor usage. If there is a way to permanently set the backlight level of the display to a lower level (like 20%), I can live with that as well.