acpi_backlight=video does not work

[Kamal Mostafa]

[Ubuntu 10.04 LTS kernel through upstream kernel version 2.6.34-rc6]

Kernel boot param "acpi_backlight=video" does not enable backlight support as intended. Setting it actually ends up enabling the video output switching feature (the same as "acpi_display_output=video" does).

It is not possible to force backlight support, since no code ever enables ACPI_VIDEO_BACKLIGHT_FORCE_VIDEO.

[Kamal Mostafa (kamalmostafa)]

The attached patch has been submitted to the linux-kernel and kernel-team mailing lists.

[Steve Conklin (sconklin)]

SRU Justification

Impact: The upstream process for stable tree updates is quite similar in scope to the Ubuntu SRU process, e.g., each patch has to demonstrably fix a bug, and each patch is vetted by upstream by originating either directly from Linus' tree or in a minimally backported form of that patch.

The 2.6.32.21 upstream stable patch set is now available and contains fixes for this problem. It should be included in the Ubuntu kernel as well.

Related commits in the Lucid repo are:

27c8380 ACPI: video: fix acpi_backlight=video

[Martin Pitt (pitti)]

Accepted linux into lucid-proposed, the package will build now and be available in a few hours. Please test and give feedback here. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you in advance!

[Stefan Bader (smb)]

Can anybody affected by the bug please give feedback whether the current proposed kernel does resolve the issue? Thanks.

[Launchpad Janitor (janitor)]

This bug was fixed in the package linux - 2.6.32-25.44

---------------
linux (2.6.32-25.44) lucid-proposed; urgency=low

  [ Brad Figg ]

  * SAUCE: (no-up) Modularize vesafb -- fix initialization
    - LP: #611471

  [ Stefan Bader ]

  * Revert "SAUCE: sync before umount to reduce time taken by ext4 umount"
    - LP: #543617, #585092

  [ Steve Conklin ]

  * Revert "SAUCE: tulip: Let dmfe handle davicom on non-sparc"
    - LP: #607824

  [ Tim Gardner ]

  * [Config] Added ums-cypress to udeb
    - LP: #576066

  [ Upstream Kernel Changes ]

  * Revert "PCI quirk: Disable MSI on VIA K8T890 systems"
    - LP: #607824
  * Revert "PCI quirks: disable msi on AMD rs4xx internal gfx bridges"
    - LP: #607824
  * Revert "(pre-stable) Input: psmouse - reset all types of mice before
    reconnecting"
    - LP: #607824
  * Revert "jbd: jbd-debug and jbd2-debug should be writable"
    - LP: #607824
  * Revert "ext4: Make fsync sync new parent directories in no-journal
    mode"
    - LP: #615548
  * Revert "ext4: Fix compat EXT4_IOC_ADD_GROUP"
    - LP: #615548
  * Revert "ext4: Conditionally define compat ioctl numbers"
    - LP: #615548
  * Revert "ext4: restart ext4_ext_remove_space() after transaction
    restart"
    - LP: #615548
  * Revert "ext4: Clear the EXT4_EOFBLOCKS_FL flag only when warranted"
    - LP: #615548
  * Revert "ext4: Avoid crashing on NULL ptr dereference on a filesystem
    error"
    - LP: #615548
  * Revert "ext4: Use bitops to read/modify i_flags in struct
    ext4_inode_info"
    - LP: #615548
  * Revert "ext4: Show journal_checksum option"
    - LP: #615548
  * Revert "ext4: check for a good block group before loading buddy pages"
    - LP: #615548
  * Revert "ext4: Prevent creation of files larger than RLIMIT_FSIZE using
    fallocate"
    - LP: #615548
  * Revert "ext4: Remove extraneous newlines in ext4_msg() calls"
    - LP: #615548
  * Revert "ext4: init statistics after journal recovery"
    - LP: #615548
  * Revert "ext4: clean up inode bitmaps manipulation in ext4_free_inode"
    - LP: #615548
  * Revert "ext4: Do not zero out uninitialized extents beyond i_size"
    - LP: #615548
  * Revert "ext4: don't scan/accumulate more pages than mballoc will
    allocate"
    - LP: #615548
  * Revert "ext4: stop issuing discards if not supported by device"
    - LP: #615548
  * Revert "ext4: check s_log_groups_per_flex in online resize code"
    - LP: #615548
  * Revert "ext4: fix quota accounting in case of fallocate"
    - LP: #615548
  * Revert "ext4: allow defrag (EXT4_IOC_MOVE_EXT) in 32bit compat mode"
    - LP: #615548
  * Revert "ext4: rename ext4_mb_release_desc() to ext4_mb_unload_buddy()"
    - LP: #615548
  * Revert "ext4: Remove unnecessary call to ext4_get_group_desc() in
    mballoc"
    - LP: #615548
  * Revert "ext4: fix memory leaks in error path handling of
    ext4_ext_zeroout()"
    - LP: #615548
  * Revert "ext4: check missed return value in ext4_sync_file()"
    - LP: #615548
  * Revert "ext4: Issue the discard operation *before* releasing the blocks
    to be reused"
    - LP: #615548
  * Revert "ext4: Fix buffer head leaks after calls to
    ext4_get_inode_loc()"
    - LP: #615548
  * Revert "ex...