Comment 3 for bug 1354710

Workaround information

Reboot with only the kernel parameter acpi_backlight=vendor :
no change

output of ls /sys/class/backlight

ideapad
intel_backlight
thinkpad_screen

output of ls -la /sys/class/backlight/intel_backlight/ > lslabacklight as root

total 0
drwxr-xr-x 3 root root 0 Aug 8 23:17 .
drwxr-xr-x 4 root root 0 Aug 8 23:17 ..
-r--r--r-- 1 root root 4096 Aug 8 23:27 actual_brightness
-rw-r--r-- 1 root root 4096 Aug 8 23:27 bl_power
-rw-r--r-- 1 root root 4096 Aug 8 23:17 brightness
lrwxrwxrwx 1 root root 0 Aug 8 23:27 device -> ../../card0-LVDS-1
-r--r--r-- 1 root root 4096 Aug 8 23:17 max_brightness
drwxr-xr-x 2 root root 0 Aug 8 23:27 power
lrwxrwxrwx 1 root root 0 Aug 8 23:27 subsystem -> ../../../../../../../class/backlight
-r--r--r-- 1 root root 4096 Aug 8 23:17 type
-rw-r--r-- 1 root root 4096 Aug 8 23:17 uevent

echo 8 > /sys/class/backlight/intel_backlight/brightness
brightness changes

reboot with just kernel parameter video.use_native_backlight=1

keys still cannot be used for changing brightness

creating a new file in /usr/share/X11/xorg.conf.d/80-backlight.conf and paste into it the following code:

Section "Device"
    Identifier "Intel Graphics"
    Driver "intel"
    Option "AccelMethod" "sna"
    Option "Backlight" "intel_backlight" # use your backlight that works here
    BusID "PCI:0:2:0"
EndSection

keys can now be used for changing brightness of backlight