Arch Linux

zyaku

Member

Registered: 2013-11-09

Posts: 5

Intel Backlight Issues on 2014 Macbook Air

Hello, I'm running Arch Linux on a 2014 Macbook Air. I am experiencing this bizarre bug with the backlight.

When I first boot the laptop, the backlight behaves normally. I can use xbacklight to change the backlight settings as expected. However, when I suspend to memory and then wake up the computer, something very strange happens:

If the backlight is set to about 80% or higher in software, then the hardware is at 100% brightness. However, if the backlight is below 80% in software, then the hardware backlight turns off completely.

I've tried a lot of things for this bug, including pretty much every combination of kernel options and xorg configurations I could find online. A few of them are here: https://wiki.archlinux.org/index.php/Backlight . Interestingly enough, I only have this problem when I use suspend to memory. If I use the linux kernel's freeze, standby, or hibernate states, then the backlight comes back on as expected. I've tried using userspace power managers, but the problem remained the same.

Here is the pertinent output lspci -k:

00:02.0 VGA compatible controller: Intel Corporation Haswell-ULT Integrated Graphics Controller (rev 09)
	Subsystem: Apple Inc. Device 011b
	Kernel driver in use: i915
	Kernel modules: i915

The backlight controls for my computer live in /sys/class/backlight/intel_backlight . It contains these files:

actual_brightness  brightness  max_brightness  subsystem  uevent
bl_power	   device      power	       type

'cat max_brightness' gives 2777. When I set brightness to 2249 (a little bit more than %80) with 'echo 2249 > brightness', it comes on full brightness. When I set it to 2247, it's all the way off, and when I set it to 2248, it slowly flickers from light to dark. The actual_brightness file mirrors the brightness one-- when I set brightness to 2249, actual_brightness is 2249, and so on.

I used to have the same problem when I ran Ubuntu on an older model Macbook Air (2012, I think), so I don't think that this is a new issue.

How do I fix it? If it's just a bug, then where do I submit the bug report?

anhaedre

Member

Registered: 2014-10-26

Posts: 3

Re: Intel Backlight Issues on 2014 Macbook Air

Hi,

indeed, it's a known issue.
you can try to install mba6x_bl-dkms from the AUR.

Last edited by anhaedre (2014-11-23 16:52:47)

zyaku

Member

Registered: 2013-11-09

Posts: 5

Re: Intel Backlight Issues on 2014 Macbook Air

indeed, it's a known issue.
you can try to install mba6x_bl-dkms from the AUR.

That fixed it, although I had to write a startup script so that the backlight would get turned on when I booted . Thank you very much!

selzer

Member

From: Austria

Registered: 2014-11-29

Posts: 8

Re: Intel Backlight Issues on 2014 Macbook Air

I have the same problem on the exact same Macbook Air, but currently the fix is broken: https://github.com/patjak/mba6x_bl/issu … t-65291034.

Did you experience the same problem, and did the start script fix it?

jomuller

Member

Registered: 2015-05-30

Posts: 1

Re: Intel Backlight Issues on 2014 Macbook Air

I had the same issued and for me, the patch worked perfectly.

Upgrade

sudo pacman -Syu

Then restart if linux kernel was upgraded.

Install linux headers

sudo pacman -S linux-headers

Install the mba6x_bl-dkms patch from AUR

wget https://aur.archlinux.org/packages/mb/mba6x_bl-dkms/mba6x_bl-dkms.tar.gz
tar -xvf mba6x_bl-dkms.tar.gz
cd mba6x_bl-dkms
makepkg -i

Last edited by jomuller (2015-05-30 09:46:52)