[SOLVED] iMac 27 (mid 2011), Radeon HD 6770M brightness control

I have installed GNOME Manjaro on a iMac 27 (mid 2011) with a Radeon HD 6770M graphic card.

Although most of the thing are working I cannot change the brightness using the keyboard buttons nor the brightness slider.
I chose the free drivers during the installation of Manjaro

Because there are many suggestions on how to solve this issue, I would like to have a simple clear solution and avoid breaking the installation.

Also, I am wondering if it is really required to modify GRUB and if that might break the installation.

This post suggests to use xf86-video-ati drivers

While this one suggests to add the following lines to the GRUB configuration

acpi_backlight=video
acpi_backlight=vendor
acpi_backlight=native

Which one would you suggest?
Do I really need to add the Kernel parameters?
Should I use free or proprietary drivers?

Sorry for the many questions to a maybe simple issue.
Thanks everybody in advance!

This part is what you have to focus on:
https://wiki.archlinux.org/index.php/IMac_Aluminum#Brightness_control_on_a_2011_27_inch_iMac
The key part is to this quote

and what follows.

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Hello @bogdancovaciu, although I did not try it yet, it seems like your reply is about adjusting the brightness from the command line, which I can do already using the program brightnessctl.
What I need is a solution to let the brightness control button and sliders work (no command line).

The machine will be used by people who do not know how to use a command prompt.

Thanks a lot anyway :wink:

:slight_smile: Then you have to read that wiki carefully to understand why the ACPI calls depend on the way you boot, and how that influences it ...

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90% of issues can be solved by reading.

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I have the same iMac. Use: radeon.dpm=0 acpi_backlight=vendor.

Brightness working perfectly out of box on Manjaro 18.0.4.

2 Likes

Thanks a lot @TheRoark that is exactly what I needed :wink:

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