[Bug 103781] Intel - display brightness control not working with i915.fastboot=1

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=103781

--- Comment #14 from Arthur Borsboom <arthurborsboom at gmail.com> ---
The original problem is not the fact that the screen goes completely black. The
original problem is that the brightness cannot be changed, except after
pressing the Fn-Brightness-down for 10 or 20 times and then the screen turns
black.

I will summarize the differences by the behavior below.

-----------------------------------------------------------
Fastboot disabled (default) / everything works as expected
-----------------------------------------------------------

Brightness keys function as expected. Brightness up + down keys change the
intensity of the backlight with certain steps. Pressing the down button many
times, will lower the backlight and finally turns of the screen and results in
a black screen. 

-------------------------------------------------------------
Fastboot enabled with kernel 4.13.11 - 4.15.5 (original problem)
-------------------------------------------------------------
Pressing the brightness keys does not change the intensity of the backlight.
Pressing the brightness down key many times, results in a black screen.

-------------------------------------------------------------
Fastboot enabled with kernel 4.18.5 - 4.15.5
-------------------------------------------------------------

Pressing the brightness keys does not change the intensity of the backlight.
Pressing the brightness down key many times, does not result in a black screen
anymore. I am not sure if that is good or bad, but something did change in
comparison to previous kernels.


In other words, with fastboot enabled, I cannot change the brightness of the
screen anymore with the brightness keys, as was the case without fastboot
enabled.

Does this help sufficiently to understand the issue?

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