kernel-packages team mailing list archive

["Christopher M. Penalver" <christopher.m.penalver@xxxxxxxxx>]

Anders Kaseorg, 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-rc6

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.

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

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.

** Tags added: latest-bios-1.52

** No longer affects: gnome-settings-daemon (Ubuntu)

** Changed in: linux (Ubuntu)
   Importance: Undecided => Low

** Changed in: linux (Ubuntu)
       Status: Confirmed => Incomplete

** Summary changed:

- Backlight brightness control regressed from logarithmic scale to linear scale
+ [Lenovo ThinkPad T510] Backlight brightness control regressed from logarithmic scale to linear scale

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https://bugs.launchpad.net/bugs/1341108

Title:
  [Lenovo ThinkPad T510] Backlight brightness control regressed from
  logarithmic scale to linear scale

Status in “linux” package in Ubuntu:
  Incomplete

Bug description:
  After upgrading from kernel 3.15.0-6 to kernel 3.16.0-3, the backlight
  became very difficult to control near the low end of the scale. The
  lowest setting now turns the backlight completely off, but the second-
  lowest setting is too bright. Meanwhile, the difference between the
  highest several settings is nearly imperceptible.

  This happened because /sys/class/backlight/acpi_video0/brightness has
  disappeared in kernel 3.16 in favor of
  /sys/class/intel_backlight/brightness. But the relationship between
  acpi_video0 and intel_backlight is not linear.  As acpi_video varies
  [0,1,2,…,13,14,15], intel_backlight varies as
  [52,87,139,…,2557,3358,4437].

  I measured the exact relationship between the two scales on kernel
  3.15 and plotted it with the intel_backlight values on a logarithmic
  scale (see attachment). You can see that the function intel_backlight
  = 60*(4/3)^acpi_video0 is a good fit.

  It’s well known that perceived brightness varies logarithmically with
  physical intensity (Fechner’s law), so it’s no surprise that the
  acpi_video0 scale was more useful. Either the kernel or GNOME should
  adjust the intel_backlight scale to logarithmic.

  (I’m running utopic on a Lenovo Thinkpad T510.)

  ProblemType: Bug
  DistroRelease: Ubuntu 14.10
  Package: linux-image-3.16.0-3-generic 3.16.0-3.8
  ProcVersionSignature: Ubuntu 3.16.0-3.8-generic 3.16.0-rc4
  Uname: Linux 3.16.0-3-generic x86_64
  NonfreeKernelModules: openafs
  ApportVersion: 2.14.4-0ubuntu2
  Architecture: amd64
  AudioDevicesInUse:
   USER        PID ACCESS COMMAND
   /dev/snd/controlC0:  anders     2179 F.... pulseaudio
  CurrentDesktop: GNOME
  Date: Sat Jul 12 07:06:12 2014
  EcryptfsInUse: Yes
  HibernationDevice: RESUME=UUID=fd305e7c-c58c-4061-8105-5cda63c38849
  InstallationDate: Installed on 2010-12-05 (1315 days ago)
  InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Alpha amd64 (20101202)
  MachineType: LENOVO 4313CTO
  ProcFB: 0 inteldrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.16.0-3-generic root=/dev/mapper/fdisk-ubuntu ro init=/lib/systemd/systemd quiet splash crashkernel=384M-:128M crashkernel=384M-:128M vt.handoff=7
  RelatedPackageVersions:
   linux-restricted-modules-3.16.0-3-generic N/A
   linux-backports-modules-3.16.0-3-generic  N/A
   linux-firmware                            1.132
  SourcePackage: linux
  UpgradeStatus: Upgraded to utopic on 2013-10-31 (254 days ago)
  dmi.bios.date: 09/26/2012
  dmi.bios.vendor: LENOVO
  dmi.bios.version: 6MET92WW (1.52 )
  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:bvr6MET92WW(1.52):bd09/26/2012:svnLENOVO:pn4313CTO:pvrThinkPadT510:rvnLENOVO:rn4313CTO:rvrNotAvailable:cvnLENOVO:ct10:cvrNotAvailable:
  dmi.product.name: 4313CTO
  dmi.product.version: ThinkPad T510
  dmi.sys.vendor: LENOVO

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