Comment 125 for bug 1098216

I just tested it on my Thinkpad X1 (haswell) and the fix works.
However, there is a side effect. Connecting and Disconnecting the
Power resets the brightness to maximum. Not sure how to go about
working around this.

anmar

On 26 February 2014 23:14, madbiologist <email address hidden> wrote:
> The upstream 3.14-rc4 kernel also contains this commit:
>
> author Rafael J. Wysocki
> committer Rafael J. Wysocki
> commit a6940190ac15c361862a1a8f50a2072db7184749
> tree c73be15646c6418f77a94fede3afc7eabd589dd6
> parent 0e9f81d3b7cd0649a3bc437391b6a0650f98f844
>
> Revert "ACPI: Blacklist Win8 OSI for some HP laptop 2013 models"
>
> This reverts commit 2d4054d84224 (ACPI: Blacklist Win8 OSI for some HP
> laptop 2013 models) that is not necessary any more after previous commit
> 1811fcb029fa (ACPI / video: Add systems that should favour native
> backlight interface).
>
> Requested-by: Takashi Iwai
> Tested-by: Mika Westerberg
> Signed-off-by: Rafael J. Wysocki
>
> --
> You received this bug notification because you are subscribed to a
> duplicate bug report (1121951).
> https://bugs.launchpad.net/bugs/1098216
>
> Title:
> Regression in brightness control on Lenovo Thinkpad X230 (+tablet) and
> X1 Carbon
>
> Status in The Linux Kernel:
> In Progress
> Status in “linux” package in Ubuntu:
> Triaged
> Status in “linux” package in Fedora:
> Unknown
>
> Bug description:
> == Raring SRU Justification ==
>
> Impact: A number of ThinkPad models have a workaround in the ACPI
> backlight implementation for Windows 8 that more or less completely
> breaks backlight control.
>
> Fix: Add an OSI quirk to no longer claim to be Windows 8 on these
> machines, causing the firmware to revert to the older, working behavior.
>
> Test Case: Verified on LP #1098216 and bugzill.kernel.org #51231.
>
> ---
>
> Something changed between the 3.5 and the 3.7 kernel, leading to
> broken brightness control on my Thinkpad x230.
>
> Here are some test results:
> == 3.5.0-21-generic ==
> === Post-boot values ===
> /sys/class/backlight:
> - intel-backlight
> + actual_brightness => 4438
> + bl_power => 0
> + brightness => 4438
> + max_brightness => 4438
> - acpi_video0
> + actual_brightness => 15
> + bl_power => 0
> + brightness => 15
> + max_brightness => 15
>
> === Tests ===
> echo 0 > acpi_video0/brightness => works
> echo 0 > intel_backlight/brightness => works
>
> == 3.8.0-0-generic ==
> === Post-boot values ===
> /sys/class/backlight:
> - intel-backlight
> + actual_brightness => 4438
> + bl_power => 0
> + brightness => 4438
> + max_brightness => 4438
> - acpi_video0
> + actual_brightness => 100
> + bl_power => 0
> + brightness => 100
> + max_brightness => 100
>
> === Tests ===
> echo 0 > acpi_video0/brightness => doesn't do anything
> echo 0 > intel_backlight/brightness => works
> ---
> ApportVersion: 2.8-0ubuntu1
> Architecture: amd64
> CheckboxSubmission: 12108b8b8b67d760cdd84f1b9574e7f3
> CheckboxSystem: bb422ca46d02494cdbc459927a98bc2f
> DistroRelease: Ubuntu 13.04
> InstallationDate: Installed on 2012-09-02 (129 days ago)
> InstallationMedia: Ubuntu 12.10 "Quantal Quetzal" - Alpha amd64 (20120902)
> MarkForUpload: True
> Package: linux (not installed)
> ProcEnviron:
> LANGUAGE=en_US:en
> TERM=xterm
> PATH=(custom, no user)
> LANG=en_US.UTF-8
> SHELL=/bin/bash
> ProcVersionSignature: Ubuntu 3.8.0-0.1-generic 3.8.0-rc3
> Tags: raring
> Uname: Linux 3.8.0-0-generic x86_64
> UnreportableReason: The running kernel is not an Ubuntu kernel
> UpgradeStatus: No upgrade log present (probably fresh install)
> UserGroups:
>
> WORKAROUND:
>
> Add to /etc/default/grub
> in the variable "GRUB_CMDLINE_LINUX_DEFAULT":
>
> acpi_osi=\"!Windows 2012\"
>
> e.g:
>
> GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_osi=\"!Windows 2012\""
>
> Then run "sudo update-grub".
>
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