Arch Linux User Repository

Hi jiri.one, thanks for the info. From that reddit thread,

PowerDevil cannot deal with more than one brightness source,

so

while both of the monitors change their brightness value on the same scale (from 0 to 100), the effective brightness is different because the two have different backlight illumination at the same value.

For example, my brightness values usually are 65 for laptop screen and 40 for external monitor. As far as I understand I can't independently manage brightness values for different monitors without this dkms. I would be glad if I'm wrong.

And, without this dkms there is no backlight device in /sys/class/backlight for my external monitor.

This dkms is no more needed, because now is powerdevil compiled with

-DHAVE_DDCUTIL=On

But still is needed to have i2c_dev loaded before sddm, so the systemd unit, which I am using is:

[Unit]
After=multi-user.target
Before=sddm.service

[Service]
Type=oneshot
ExecStart=/usr/bin/modprobe i2c_dev
ExecStop=/usr/bin/modprobe --remove i2c_dev
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target

More info is here: https://www.reddit.com/r/kde/comments/epgs13/kde_my_journey_to_get_a_brighness_slider_for_my/

Andrej.Korshikov thanks a lot for your comment, it really helped me.

/etc/systemd/system/ddcci-backlight.service:

# Placing "ddcci_backlight" into /etc/modules-load.d
# leads to hang on boot with external (HDMI) monitor
# connected to the laptop, so we need to add the module later.

# And ddcci_backlight can't detect monitor during sddm.service startup.

[Unit]
After=multi-user.target
Before=sddm.service

[Service]
Type=oneshot
ExecStart=/usr/bin/modprobe ddcci_backlight
ExecStop=/usr/bin/modprobe --remove ddcci_backlight
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target

@Chrissss What if you have a linux-lts kernel?

dkms already has an optional dependency on all the kernels in the repository.

I think the linux-headers should be a dependecy. Without them I get the following error, when installing the PKGBUILD:

[...]
(2/3) Install DKMS modules
==> Unable to install module ddcci/0.3.3 for kernel *: Missing kernel headers.
(3/3) Removing old cached pacakges...
[...]

After running pacman -S linux-headers the module gets built and installed successfully.

Would you consider including my patch: https://gitlab.com/ddcci-driver-linux/ddcci-driver-linux/merge_requests/3 (raw diff: https://gitlab.com/mickael9/ddcci-driver-linux/commit/a05b4ec96328fda73aa4177f561dc69872061822.diff) ?