Debian 9 stretch can't adjust laptop monitor brightness with fn keys

Question

Laptop Model: HP Pavilion dv6 2170ee

I could change monitor brightness by fn + f7 / f8 keys in Debian 7 wheezy.

But since I installed Debian 9 stretch, seemingly, these keys do not work. Even in Mate Power Manager there's no slider to change brightness. I searched a bit. Like these pages:

Fn keys can't adjust brightness MATE desktop

Brightness fn key shortcut doesn't work on ASUS laptop

When I run acpi_listen and press fn + f7 / f8 keys, I get:

khosrow@hpx:~$ acpi_listen
video/brightnessdown BRTDN 00000087 00000000
video/brightnessup BRTUP 00000086 00000000

So I guess the keys work, but the brightness doesn't change. Any idea how to fix this?

Answer 1

Can you post your /etc/default/grub file? I have a potential solution:

In /etc/default/grub, change

GRUB_CMDLINE_LINUX_DEFAULT="quiet"

to

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=native pcie_aspm=force acpi_osi="

That enabled my ability to change the backlight with my Fn keys, with some side effects. Read more about that here: Need help configuring ASUS G75VW NVidia Debian 9 brightness: How do I get my Fn keys to change the brightness AND keep the slider in the top right?