kernel-packages team mailing list archive

[Seth Forshee <seth.forshee+lp@xxxxxxxxxxxxx>]

I looked into the screen brightness issue a little bit a while back. The
reason that the brightness gets set to maximum at boot is that the
firmware doesn't initialize some state memory with the brightness at
boot, so when the brightness is read from the firmware it gets back a
value which corresponds to the maximum brightness. When Linux boots the
acpi_video driver does some tests of various functionality which
includes reading the current brightness and writing it back, which has
the effect of setting the screen brightness to maximum.

What OS X seems to do is to write the screen brightness to an EFI
variable, so either acpi_video would need to know to look for that
variable or else acpi_video just shouldn't be used for brightness on
Apple hardware. As a workaround you could pass acpi_backlight=vendor on
the kernel command line to disable use of the ACPI backlight interface.

Not sure about the keyboard backlight, but it could be something
similar.

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https://bugs.launchpad.net/bugs/1279308

Title:
  [MacBook Air 6,2] screen backlight brightness and keyboard light turn
  into fully-on after Grub boot with i915 driver

Status in “linux” package in Ubuntu:
  Incomplete

Bug description:
  Problem: Both the screen backlight brightness and keyboard light are
  turned on during the booting as tested on ubuntu 12.04.3, 12.04.4, and
  13.10. Due to installation problem on 12.04, it's only tested with the
  live system.

  What's expected: the brightness state before booting is preserved.

  Some trials: the problem should be on i915 driver even in single user mode. Tried "nomodeset" kerenel arguement can avoid the problem, but X will fail to start.
  --- 
  ApportVersion: 2.12.5-0ubuntu2
  Architecture: amd64
  AudioDevicesInUse:
   USER        PID ACCESS COMMAND
   /dev/snd/controlC0:  john       1776 F.... pulseaudio
   /dev/snd/controlC1:  john       1776 F.... pulseaudio
  DistroRelease: Ubuntu 13.10
  InstallationDate: Installed on 2014-02-10 (1 days ago)
  InstallationMedia: Ubuntu 13.10 "Saucy Salamander" - Release amd64 (20131016.1)
  MachineType: Apple Inc. MacBookAir6,2
  MarkForUpload: True
  NonfreeKernelModules: wl
  Package: linux (not installed)
  ProcFB: 0 inteldrmfb
  ProcKernelCmdLine: BOOT_IMAGE=/@/boot/vmlinuz-3.11.0-15-generic.efi.signed root=UUID=b52fef82-3749-4624-a352-bd750dcb7e65 ro rootflags=subvol=@ quiet splash vt.handoff=7
  ProcVersionSignature: Ubuntu 3.11.0-15.25-generic 3.11.10
  RelatedPackageVersions:
   linux-restricted-modules-3.11.0-15-generic N/A
   linux-backports-modules-3.11.0-15-generic  N/A
   linux-firmware                             1.116
  Tags:  saucy
  Uname: Linux 3.11.0-15-generic x86_64
  UpgradeStatus: No upgrade log present (probably fresh install)
  UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo
  dmi.bios.date: 11/12/2013
  dmi.bios.vendor: Apple Inc.
  dmi.bios.version: MBA61.88Z.0099.B07.1311121319
  dmi.board.asset.tag: Base Board Asset Tag#
  dmi.board.name: Mac-7DF21CB3ED6977E5
  dmi.board.vendor: Apple Inc.
  dmi.board.version: MacBookAir6,2
  dmi.chassis.type: 10
  dmi.chassis.vendor: Apple Inc.
  dmi.chassis.version: Mac-7DF21CB3ED6977E5
  dmi.modalias: dmi:bvnAppleInc.:bvrMBA61.88Z.0099.B07.1311121319:bd11/12/2013:svnAppleInc.:pnMacBookAir6,2:pvr1.0:rvnAppleInc.:rnMac-7DF21CB3ED6977E5:rvrMacBookAir6,2:cvnAppleInc.:ct10:cvrMac-7DF21CB3ED6977E5:
  dmi.product.name: MacBookAir6,2
  dmi.product.version: 1.0
  dmi.sys.vendor: Apple Inc.

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