Comment # 63 on bug 899879 from Freek de Kruijf

(In reply to Egbert Eich from comment #61)
> Can you get the value from 'brighness' right after a boot?

It is 4687, max_brightness is 7812.

> This is wrong: if you want to specify the '-n' option it needs to be at the
> beginning of the command line.

Did not seem to be of any harm.

> > For the above I only removed nomodeset from the command line. Should I add
> > systemd.restore_state=0 and repeat?
> 
> This just prevents the previously saved value to be restored.
> 
> Can you try the following? If you reboot after your Plasma5 session went
> black,
> and don't specify this option on the next reboot, your will get a black
> login screen after the reboot.

Yesterday with your newest xf86-video-intel module, version
2.99.917.590_g094924f-168.1, and nomodeset removed from the boot command, I did
not get a black screen any more. However it causes a lot of output to
/var/log/Xorg.0.log. This file does not contain a failing dbus message any
more.

At this moment, same as above, I again hear the sound of an active Plasma5
session, but the screen is black; brightness is at its maximum.
I tried different values for brightness and found that 0 gives black, maximum
gives black, close to maximum 7500 gives a dim screen, 4687 gives a bright
screen. Seems we have found culprit.

I will try the xf86-video-intel from the main repository.