[arch-general] ddcutil not working with nvidia card

[ente]

On Tue, 2018-01-23 at 14:02 +0000, Foxtrot Mike via arch-general wrote:
> 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-lin
> e_options

Never used ddcutil. Have a look at xrandr --brightness. Works perfectly
for me on my OLED without backlight functionality. The following
example gives u 30% brightness:
	xrandr --output DVI-0 --brightness 0.3

I think xrandr works on Wayland, although I cant currently test it. It
works on my NVidia / LCD setup. Although on this setup it makes
less sense: the actual backlight stays at 100%, just the colors are adjusted.
On an OLED without backlight the solution works 100% smooth. Check the
wiki pages on HP x360 laptop [1]. There is also a script available linking /sys/class/backlight/intel_backlight to xrandr brightness in case you have brightness hardware keys.

regards,

ente

[1] https://wiki.archlinux.org/index.php/HP_Spectre_x360_13-4231ng