After the last `apt-get update` the screen backlight is turned off.

[Sebo]

Cause: After the last `apt-get update` and system `reboot` the screen backlight is turned off.
Expected: The screen is expected to have the backlight turned on or at least to be able to set it on.

Comment:
The last update has updated the linux kernel and kernel headers package. After booting up with the new kerlnel the screen backlight has turned off after a second (right after the system boot). I have not found any way to torn it on, no mether if I increase or decrease the backlight setting and no mether if the system is working on batery or with the power cord attached.
I am running Ubuntu Desktop 14.04 LTS at Dell Vostro-5470.

$ uname -a
Linux Vostro-5470 3.13.0-32-generic #57-Ubuntu SMP Tue Jul 15 03:51:08 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
$ lsb_release -rd
Description: Ubuntu 14.04.1 LTS
Release: 14.04

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: linux-image-3.13.0-32-generic 3.13.0-32.57 [modified: boot/vmlinuz-3.13.0-32-generic]
ProcVersionSignature: Ubuntu 3.13.0-32.57-generic 3.13.11.4
Uname: Linux 3.13.0-32-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.4
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC1: sebo 2267 F.... pulseaudio
 /dev/snd/pcmC1D0p: sebo 2267 F...m pulseaudio
 /dev/snd/controlC0: sebo 2267 F.... pulseaudio
CurrentDesktop: Unity
Date: Wed Sep 17 09:02:17 2014
EcryptfsInUse: Yes
InstallationDate: Installed on 2014-08-08 (39 days ago)
InstallationMedia: Ubuntu 14.04.1 LTS "Trusty Tahr" - Release amd64 (20140722.2)
MachineType: Dell Inc. Vostro 5470
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-3.13.0-32-generic root=/dev/mapper/ubuntu--vg-root ro quiet splash vt.handoff=7
RelatedPackageVersions:
 linux-restricted-modules-3.13.0-32-generic N/A
 linux-backports-modules-3.13.0-32-generic N/A
 linux-firmware 1.127.5
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 08/09/2013
dmi.bios.vendor: Dell Inc.
dmi.bios.version: A00
dmi.board.name: 0RYY7X
dmi.board.vendor: Dell Inc.
dmi.board.version: A00
dmi.chassis.type: 8
dmi.chassis.vendor: Dell Inc.
dmi.chassis.version: 0.1
dmi.modalias: dmi:bvnDellInc.:bvrA00:bd08/09/2013:svnDellInc.:pnVostro5470:pvr:rvnDellInc.:rn0RYY7X:rvrA00:cvnDellInc.:ct8:cvr0.1:
dmi.product.name: Vostro 5470
dmi.sys.vendor: Dell Inc.

[Sebo (sebo-pl+ubuntu-com)]

This should be clasified as regression issue.

[Brad Figg (brad-figg)]

This change was made by a bot.

[Sebo (sebo-pl+ubuntu-com)]

This should be clasified as regression issue cause reverting to the previous kernel do fix the issue.

[Joseph Salisbury (jsalisbury)]

I'd like to perform a bisect to figure out what commit caused this regression. We need to identify the earliest kernel where the issue started happening as well as the latest kernel that did not have this issue.

Can you test the following upstream kernels and report back?

v3.13.11.5: http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.13.11.5-trusty/
v3.13.11.6: http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.13.11.6-trusty/

[Sebo (sebo-pl+ubuntu-com)]

With v3.13.11.5 the screen backlight is tourned on :)

However I have noticed that the backlight switch (which should let the adjustment of the backlight volume) seems not change anything.

$ uname -a
Linux Vostro-5470 3.13.11-03131105-generic #201407181735 SMP Fri Jul 18 21:35:58 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux

[Joseph Salisbury (jsalisbury)]

Great, so we can bisect between 3.13.11.5 and 3.13.11.6. Before starting the bisect, can you also test the latest 3.13 upstream stable kernel to see if the bug has been fixed:

http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.13.11.7-trusty/

[Sebo (sebo-pl+ubuntu-com)]

Thats what I just wonted to write. The update to the most recent one seems to fix the issue.
However what I might not noticed before is that this backlight adjustment is not changing anything.

[Launchpad Janitor (janitor)]

[Expired for linux (Ubuntu) because there has been no activity for 60 days.]