Comment 6 for bug 1683445

This issue can be reproduced on another E6430 here, with the same A18 BIOS / 4.10.0-19 kernel. (But the interesting thing is that it cannot be reproduced with its variant, E6430ATG, even if they're all I+N config, and using the same BIOS)

Some debug info with the 4.11rc7 mainline kernel
kernel@kernel-Latitude-E6430:~$ ls /sys/class/backlight/
intel_backlight nv_backlight
kernel@kernel-Latitude-E6430:~$ uname -a
Linux kernel-Latitude-E6430 4.11.0-041100rc7-generic #201704161731 SMP Sun Apr 16 21:32:58 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux