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[Hans Deragon <hans@xxxxxxxxxxx>]

Copying here my own observations about the problem, from my previous bug
report #1389215, now marked as a duplicate of this one.

--->

Brightness controls are not working in Unity / Xorg. When pressing the
keys <fn><home> and <fn><end> on my Lenovo W510, I see the indicator on
the screen showing the level of brightness changing, so key mapping is
not the problem. However, the brightness is not changing.

On the kernel level, I have the single following device:

# cd /sys/class/backlight
# ls -l
total 0
lrwxrwxrwx 1 root root 0 Nov 3 17:16 acpi_video0 -> ../../devices/pci0000:00/0000:00:03.0/0000:01:00.0/backlight/acpi_video0

When playing with the <fn><home> and <fn><end>, the value of
/sys/class/backlight/brightness changes accordingly. The screen
brightness does not change.

Performing:

# echo 10 >brightness

...does not have any effect (regardless of the value provided, 10 being
just an example).

WORKAROUND

There is an odd workaround. Simply go to the console using
<CTRL><ALT><F1> and using the <fn><home> and <fn><end> keys, brightness
then changes. Return to Unity / Xorg with <CTRL><ALT><F7> and the
selected brightness persists.

NON WORKING WORKAROUND

On the web, I read that adding:

Option "RegistryDwords" "EnableBrightnessControl=1"'

in xorg.conf might fix the problem. I do not have an xorg and when I let
the proprietary Nvidia driver generate one and add this option, X does
not start anymore.

Ubuntu 14.04.1 LTS with latest updates as of this writing.

----

I tried under KDE Plasma 5.1 (Neon) and still I could not change the
brightness of the backlight.

However, the CLI commands that fail in a terminal running under an Xorg
session work flawlessly under a console (<CTRL><ALT><F1>).

cd /sys/class/backlight/acpi_video0

echo 5 >brightness # Works under the console!
echo 10 >brightness # Works under the console!

This all suggest that somehow, Xorg is inhibiting the brightness
control.

----

Found out that brightness control works fine with Nouveau driver, but
not with Nvidia proprietary driver.

----

Discovered another behaviour. If you play with the brightness controls
under Xorg, nothing changes. However, suspend the computer and resume
it, and the brightness will be setup to the last setup you left when
playing with the brightness controls. Thus, the value in the kernel
persists.

You can also test this with the CLI:

# cd /sys/class/backlight/acpi_video0
# echo 10 >brightness # Nothing happens
# cat actual_brightness
10
# echo 5 >brightness # Nothing happens
# cat actual_brightness
5

<suspend computer>
<resume computer>

Now the brightness level is set to 5 and the screen finds itself at that
level.

In the backend, the controls are changing the brightness levels, it is
just that during an Xorg Session with NVIDIA proprietary drivers, the
screen's real brightness is not updated. As if the hardware signal to
the screen is never sent, except when in the console or upon resume.

----

I replaced the official proprietary NVIDIA driver nvidia-331 with
nvidia-340 from xorg-edgers and the problem persists. nvidia-340
(340.76) is the latest driver for the legacy card Quadro FX 880M of my
Lenovo W510.

----

I tried acpi_backlight=vendor on grub to novail. It even stopped working
on the TTY. Putting grub as it was restored the functionality back in
the TTY. Under X11, the problem persists.

<----

-- 
You received this bug notification because you are a member of Desktop
Packages, which is subscribed to nvidia-graphics-drivers in Ubuntu.
https://bugs.launchpad.net/bugs/562005

Title:
  Backlight controls of laptops with NVIDIA NVS and Quadro FX 880M GPUs
  no longer function while using proprietary drivers

Status in Ubuntu Certification Programme:
  Invalid
Status in nvidia-graphics-drivers package in Ubuntu:
  Invalid

Bug description:
  The brightness controls of laptops with NVIDIA NVS 3100M or Quadro FX
  880M GPUs work  while running Nouveau or when using a text mode VT,
  but not while running X and using proprietary NVIDIA drivers.  It is
  possible to force the NVIDIA driver to control the backlight by adding
  [Option "RegistryDwords" "EnableBrightnessControl=1"] to the "Devices"
  section of xorg.conf . While this allows the backlight to be
  controlled, the increments are inconsistent and often result in a
  buzzing noise from the LED backlight on Lenovo ThinkPad T510s and
  W510s. Since this did not occur while running nouveau or when
  switching in text VT, something is wrong.

  This bad backlight behaviour has been confirmed on ThinkPad models T510 and W510 with NVIDIA NVS 3100m and Quadro FX 880M chipsets, respectively, via http://www.thinkwiki.org/wiki/Category:T510
  Because this issue is related to NVIDIA's proprietary video driver, this issue can only be solved by them. An NVIDIA developer has said he will investigate the issues, which are  discussed on the nvnews.net forums at http://www.nvnews.net/vbulletin/showthread.php?t=145105 and http://www.nvnews.net/vbulletin/showthread.php?t=150069 . For future reference, the latest NVIDIA drivers can be found in the Ubuntu X-Swat X updates PPA: https://launchpad.net/~ubuntu-x-swat/+archive/x-updates

  
  ProblemType: Bug
  DistroRelease: Ubuntu 10.04
  Package: nvidia-current 195.36.15-0ubuntu2
  ProcVersionSignature: Ubuntu 2.6.32-19.28-generic 2.6.32.10+drm33.1
  Uname: Linux 2.6.32-19-generic x86_64
  NonfreeKernelModules: nvidia
  Architecture: amd64
  Date: Mon Apr 12 23:48:02 2010
  DkmsStatus:
   nvidia-current, 195.36.15, 2.6.32-19-generic, x86_64: installed
  EcryptfsInUse: Yes
  GdmLog1:

  MachineType: LENOVO 4313CTO
  ProcCmdLine: BOOT_IMAGE=/bhostnamet/vmlinuz-2.6.32-19-generic rhostnamet=UUID=0b95b314-337f-49aa-86f9-6423e76e9f20 ro
  ProcEnviron:
   LANG=en_CA.utf8
   SHELL=/bin/bash
  SourcePackage: nvidia-graphics-drivers
  XorgLogOld:

  dmi.bios.date: 02/22/2010
  dmi.bios.vendor: LENOVO
  dmi.bios.version: 6MET49WW (1 tp-smapi, 0.40, 2.6.32-19-generic, x86_64: installed
   vboxnetadp, 3.1.6, 2.6.32-19-generic, x86_64: installed
   vboxnetflt, 3.1.6, 2.6.32-19-generic, x86_64: installed
   vboxdrv, 3.1.6, 2.6.32-19-generic, x86_64: installed.12 )
  dmi.board.name: 4313CTO
  dmi.board.vendor: LENOVO
  dmi.board.version: Not Available
  dmi.chassis.asset.tag: No Asset Information
  dmi.chassis.type: 10
  dmi.chassis.vendor: LENOVO
  dmi.chassis.version: Not Available
  dmi.modalias: dmi:bvnLENOVO:bvr6MET49WW(1.12):bd02/22/2010:svnLENOVO:pn4313CTO:pvrThinkPadT510:rvnLENOVO:rn4313CTO:rvrNotAvailable:cvnLENOVO:ct10:cvrNotAvailable:
  dmi.product.name: 4313CTO
  dmi.product.version: ThinkPad T510
  dmi.sys.vendor: LENOVO
  system:
   distro:             Ubuntu
   codename:           lucid
   architecture:       x86_64
   kernel:             2.6.32-19-generic

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