[Toshiba Satellite Z930-164] Backlight control does not work, but there are entries in /sys/class/backlight

[Florent Flament]

Following bug reporting process:
https://wiki.ubuntu.com/Kernel/Debugging/Backlight#Reporting_Backlight_Bugs

Running Ubuntu 14.04 with Unity.

Testing for a work around:

* With kernel parameter acpi_backlight=vendor
  -> Brightness control is working with both applet and hotkeys.

  - # echo 8 > /sys/class/backlight/intel_backlight/brightness
    -> The command sets the screens brightness very low (almost turns
       it off).

* With kernel parameter video.use_bios_initial_backlight=0
  -> Brightness control is neither working with applet nor hotkeys.

* With kernel parameter video.use_native_backlight=1
  -> Brightness control is working with both applet and hotkeys.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: linux-image-3.13.0-30-generic 3.13.0-30.54
ProcVersionSignature: Ubuntu 3.13.0-30.54-generic 3.13.11.2
Uname: Linux 3.13.0-30-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.2
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: florent 2107 F.... pulseaudio
CurrentDesktop: Unity
Date: Sat Jun 28 18:17:42 2014
EcryptfsInUse: Yes
HibernationDevice: RESUME=/dev/mapper/toshnux--vg-swap_1
MachineType: TOSHIBA SATELLITE Z930
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.13.0-30-generic root=/dev/mapper/hostname--vg-root ro splash quiet acpi_backlight=vendor vt.handoff=7
RelatedPackageVersions:
 linux-restricted-modules-3.13.0-30-generic N/A
 linux-backports-modules-3.13.0-30-generic N/A
 linux-firmware 1.127.4
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 04/04/2013
dmi.bios.vendor: TOSHIBA
dmi.bios.version: Version 6.70
dmi.board.asset.tag: 0000000000
dmi.board.name: SATELLITE Z930
dmi.board.vendor: TOSHIBA
dmi.board.version: Version A0
dmi.chassis.asset.tag: 0000000000
dmi.chassis.type: 10
dmi.chassis.vendor: TOSHIBA
dmi.chassis.version: Version 1.0
dmi.modalias: dmi:bvnTOSHIBA:bvrVersion6.70:bd04/04/2013:svnTOSHIBA:pnSATELLITEZ930:pvrPT23LE-01900EFR:rvnTOSHIBA:rnSATELLITEZ930:rvrVersionA0:cvnTOSHIBA:ct10:cvrVersion1.0:
dmi.product.name: SATELLITE Z930
dmi.product.version: PT23LE-01900EFR
dmi.sys.vendor: TOSHIBA

[Brad Figg (brad-figg)]

This change was made by a bot.

[Michele Kipiel (michele-kipiel)]

Same here!

HW: Dell XPS13
OS: Ubuntu 14.04 64bit
What's wrong: No backlight control

[penalvch (penalvch)]

Florent Flament, could you please test the latest upstream kernel available from the very top line at the top of the page (not the daily folder) following https://wiki.ubuntu.com/KernelMainlineBuilds ? It will allow additional upstream developers to examine the issue. Once you've tested the upstream kernel, please comment on which kernel version specifically you tested. If this bug is fixed in the mainline kernel, please add the following tags:
kernel-fixed-upstream
kernel-fixed-upstream-VERSION-NUMBER

where VERSION-NUMBER is the version number of the kernel you tested. For example:
kernel-fixed-upstream-3.16-rc3

This can be done by clicking on the yellow circle with a black pencil icon next to the word Tags located at the bottom of the bug description. As well, please remove the tag:
needs-upstream-testing

If the mainline kernel does not fix this bug, please add the following tags:
kernel-bug-exists-upstream
kernel-bug-exists-upstream-VERSION-NUMBER

As well, please remove the tag:
needs-upstream-testing

Once testing of the upstream kernel is complete, please mark this bug's Status as Confirmed. Please let us know your results. Thank you for your understanding.

[Florent Flament (florentflament)]

Oh this bug is fixed upstream (Linux 3.16-rc3), thanks !
Florent

[Florent Flament (florentflament)]

Ok, I followed the 'Reverse bisecting upstream kernel versions' section and found that:
* v3.15.3-utopic is the last bad version
* v3.16-rc1-utopic is the first good version.

Working on 'Reverse commit bisecting upstream kernel versions' ...

[Florent Flament (florentflament)]

Hi Christopher,
I eventually managed to find the fix commit (this took me ages).

$ git bisect bad
751109aad5834375ca9ed0dcfcd85a00cbf872b5 is the first bad commit
commit 751109aad5834375ca9ed0dcfcd85a00cbf872b5
Author: Rafael J. Wysocki <email address hidden>
Date: Thu Jun 5 22:47:35 2014 +0200

    ACPI / video: Change the default for video.use_native_backlight to 1

    Now that we're hoping to have resolved all of the problems with
    video.use_native_backlight=1, make that the default at last.

    Link: http://marc.info/?l=linux-acpi&m=139716088401106&w=2
    Signed-off-by: Rafael J. Wysocki <email address hidden>

:040000 040000 d8f9ae057c052cd94f1adcfc0b298db2c728a315 933b38080034b141fc0c31f54f38f5b232f69c17 M drivers