Well I figured out that this issue is present in any laptop I was able to test, 
I tried with several laptops with new and not so new hardware and it is always 
the same. Asus, MSI, Lenovo, HP and Compaq, Dell, Toshiba, Intel Classmate 
Netbooks have the same problem after kernel 3.17.
Is there anything else that I could try?


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  Cannot get lowest brightness with any kernel above 3.17

Status in Linux Mint:
Status in linux package in Ubuntu:
Status in Fedora:

Bug description:
  I have been using kernel 3.16 in my Dell Laptop for a long time with
  Linux Mint 17 and previous versions and the problem here had never
  happened until LM18.

  Very often I set the lowest possible brightness, for example at night,
  or while I am flying for many hours. Using values from 0 to 4882 I
  used to run this command:

  # ie: Set lowest possible backlight brightness
  echo 0 > /sys/class/backlight/intel_backlight/brightnes

  I have always used intel_backlight instead of dell_backlight because
  it gives much more steps.

  Well now with kernel 4.4.0-53-generic it actually decreases the
  brightness but at night it is still very high even at 0 compared to
  the brightness levels I used to get with the same command. In fact,
  using a value of 0 with older kernels, the backlight is turned off.

  Just for testing, I have booted my laptop with Debian Live kernel
  3.16.0-4-amd64 and it works perfectly. Nevertheless I was able to
  reproduce the issue on newer ubuntu releases and Fedora 25.3.1. That
  is how I realized that the problem was the kernel.

  Does anyone know if with newer kernels > 3.19 this is a well-known and
  tolerated behavior? Maybe the kernel code for intel_backlight was
  modified and ended up with this problem...

  Some system information:

  System:    Kernel: 4.4.0-53-generic x86_64 (64 bit gcc: 5.4.0)
             Desktop: Cinnamon 3.2.7 (Gtk 3.18.9-1ubuntu3.2) Distro: Linux Mint 
18.1 Serena

  Machine:   System: Dell product: Inspiron 5520 v: A14 Bios: Dell v:
  A14 date: 05/13/2013

  CPU:       Dual core Intel Core i5-3210M (-HT-MCP-) cache: 3072 KB

  Graphics:  Card: Intel 3rd Gen Core processor Graphics Controller
             Display Server: X.org 1.18.4 driver: intel

  $ ls /sys/class/backlight/
  dell_backlight  intel_backlight

  Also I always use the acpi_backlight=vendor kernel parameter and I can
  confirm that by changing its value, the problem persists.

  Thanks for your time, Frk.

  P.S. I have also asked about this issue without luck here => 
  ApportVersion: 2.20.1-0ubuntu2.5
  Architecture: amd64
   /dev/snd/controlC0:  betops     6791 F.... pulseaudio
  CurrentDesktop: X-Cinnamon
  DistroRelease: Linux 18.1
  HibernationDevice: RESUME=UUID=923be72b-35a8-4997-b31a-e6072b9d4a29
  InstallationDate: Installed on 2017-02-05 (66 days ago)
  InstallationMedia: Linux Mint 18.1 "Serena" - Release amd64 20161213
  MachineType: Dell Inc. Inspiron 5520
  Package: linux (not installed)
  ProcFB: 0 inteldrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.4.0-53-generic 
root=UUID=ef4672c3-b0ed-47f3-a6b6-28e4e1e22d44 ro acpi_backlight=vendor 
intel_pstate=enable acpi_osi= acpi_irq_balance
  ProcVersionSignature: Ubuntu 4.4.0-53.74-generic 4.4.30
   linux-restricted-modules-4.4.0-53-generic N/A
   linux-backports-modules-4.4.0-53-generic  N/A
   linux-firmware                            1.157.8
  Tags:  serena serena
  Uname: Linux 4.4.0-53-generic x86_64
  UnreportableReason: The report belongs to a package that is not installed.
  UpgradeStatus: No upgrade log present (probably fresh install)
  UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo vboxusers wireshark
  _MarkForUpload: False
  dmi.bios.date: 05/13/2013
  dmi.bios.vendor: Dell Inc.
  dmi.bios.version: A14
  dmi.board.name: 04G65K
  dmi.board.vendor: Dell Inc.
  dmi.board.version: A00
  dmi.chassis.type: 8
  dmi.chassis.vendor: Dell Inc.
  dmi.chassis.version: A14
  dmi.product.name: Inspiron 5520
  dmi.product.version: A14
  dmi.sys.vendor: Dell Inc.

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