Intel i915 and xbacklight: No outputs have backlight property

Question

When I run xbacklight I get

xbacklight 
No outputs have backlight property

I've seen other posts mentions this but I do have a /sys/class/backlight/intel_backlight. I can write to the file and this works perfectly fine

echo 1000 > /sys/class/backlight/intel_backlight/brightness # (dim)
echo 4000 > /sys/class/backlight/intel_backlight/brightness # (bright)

I'm using the Intel i915 video driver.

Answer 1

I believe this problem was fixed by updating my microcode.

https://wiki.debian.org/Microcode#Updating_CPU_microcode_within_Debian_.28Intel_or_AMD.29

This did /something/ to my i915, and now it just works.