[arch-general] ddcutil not working with nvidia card

[Foxtrot Mike]

Hi all,

With my AMD card, I was able to set my monitor's (ViewSonic VA2249, connected via DVI) brightness and contrast from command line using:

ddcutil --display 1 setvcp 12 20

Later on, I swapped AMD card with an NVIDIA one (using nvidia 387.34-20). I tried using ddcutil with this new card as well, but I got this error:

~$ sudo ddcutil detect
Failure getting EDID for /dev/i2c-5: status code=DDCRC_EDID(-3016): invalid EDID
No displays found
~$

I tried googling this error, but didn't find anything helpful.

So I tried using xbacklight instead. It didn't give any positive results either, even when I provided different kernel paramters as discribed in [1]. No matter what I do with acpi and kernel parameters,  "/sys/class/backlight/acpi_video0/brightness" doesn't give actual values. Also, 'xbacklight set' has no effect on screen brightness at all.

I also tried adding `Option "RegistryDwords" "EnableBrightnessControl=1"` in "/usr/share/X11/xorg.conf.d/10-nvidia-drm-outputclass.conf". Still keyboard brigthness keys couldn't change the brightness.

Can someone help me get ddcutil working with nvidia proprietary driver?

Regards.

[1] https://wiki.archlinux.org/index.php/Backlight#Kernel_command-line_options