Arch Linux

FYI, invoking

echo 0 > /sys/class/backlight/intel_backlight/brightness

was not necessary with the previous version.

i915.invert_brightness=1 and/or Option "Backlight" "intel_backlight" in /etc/X11/xorg.conf.d/20-intel.conf seem to fix this

Thanks for the quick answer!

This is a bit strange. After using the mentioned options once, it seem that brightness control does indeed work since then (even after reboots/poweroffs), but I have a strange flicker about every second when I dim the screen. There is not flickering at full brightness. Invoking

echo 0 > /sys/class/backlight/intel_backlight/brightness

solved the issue again, meaning no flickering and working brightness control.

yes somehow this seems to be getting more and more buggy with every kernel update and different laptops might have different fixes
https://wiki.archlinux.org/index.php/backlight

try different options/combinations'
upstream bug: https://bugs.freedesktop.org/show_bug.cgi?id=76276

It seems that the intel_backlight and acpi_video0 controls are fighting for control over your backlight. On my laptop, they always have the same settings, but this doesn't seem to be the case on yours.

I spoke too soon. While I get no flickering, the backlight control of intel_backlight is finer than acpi_video0 and can reach a higher state.

Does Kevin's suggestion of adding the explicit intel_backlight option to an xorg.conf.d file help you?

Thanks for all your feedback. I get flickering with all combinations of the options. But since I also get the flickering without even starting X, I don't think the issue will be solved with any X related settings (but like I said, I nevertheless tried).

It seems "echo 0 > /sys/class/backlight/intel_backlight/brightness" once after starting the laptop takes care of the issue. It is also not necessary to repeat that after suspend-to-ram.

What is weird is the following:

with video.use_native_backlight=1 I get

# ls /sys/class/backlight/
intel_backlight

echo 0 > /sys/class/backlight/intel_backlight/brightness # no flickering
echo 4882 > /sys/class/backlight/intel_backlight/brightness # no flickering
# anything in between and excluding 0 and 4882 flickers (4882 is the maximum), I didn't try all values for n ;)


With video.use_native_backlight=0 I get:
# ls /sys/class/backlight/
acpi_video0 intel_backlight

echo 0 > /sys/class/backlight/intel_backlight/brightness && echo m > /sys/class/backlight/acpi_video0/brightness # no flickering for all m (0-100 now for acpi), things work as they should
echo n > /sys/class/backlight/intel_backlight/brightness && echo m > /sys/class/backlight/acpi_video0/brightness # flickering for all n > 0 and n < 4882 and for all m, and also this
echo 4882 > /sys/class/backlight/intel_backlight/brightness && echo 0 > /sys/class/backlight/acpi_video0/brightness # no flickering, but also no brightness change

Since it doesn't seem to work with video.use_native_backlight=1, I'm not sure the issue is necessarily related to a battle between intel and acpi, because I get flickering even without acpi.

I guess this will be solved upstream...

I had opened #40065 that was marked as a duplicate of this bug.

With linux 3.14.6-1 my backlight is now working fine.

Can this be closed now?

Yes, it can be closed! Thanks a lot!