backlight issue with HP Envy 17 under Ubuntu 14.04

[Fabien]

Having tried all the kernel options suggested on the page https://wiki.ubuntu.com/Kernel/Debugging/Backlight I never saw the backlight files under /sys/class/backlight and the function keys are not working.

See below some info on my environment and all the degug info as per requested in the above mentioned wiki in the attached file.

Regards,
Fabien

$ uname -a
Linux HPMATE 3.16.0-33-generic #44~14.04.1-Ubuntu SMP Fri Mar 13 10:33:29 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

Kernel option from Grub : none

$ ll /sys/class/backlight
total 0
drwxr-xr-x 2 root root 0 mai 25 09:38 ./
drwxr-xr-x 55 root root 0 mai 25 09:38 ../

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: linux-image-3.16.0-33-generic 3.16.0-33.44~14.04.1
ProcVersionSignature: Ubuntu 3.16.0-33.44~14.04.1-generic 3.16.7-ckt7
Uname: Linux 3.16.0-33-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.20
Architecture: amd64
CurrentDesktop: MATE
Date: Wed May 25 09:50:46 2016
InstallationDate: Installed on 2016-05-21 (4 days ago)
InstallationMedia: Ubuntu MATE 14.04.2 "Trusty Tahr" - LTS amd64 (20150323)
SourcePackage: linux-lts-utopic
UpgradeStatus: No upgrade log present (probably fresh install)