Re: Bug#772440: Bug #772440: linux-image-3.16.0-4-amd64: Built-in display dimmed if black if external monitor is plugged in

[jre <jre.winesim@gmail.com>]

CCing debian-x@lists.debian.org and especially Maximillan Attems who
prepared xserver-xorg-video-intel 2:2.99.911-git20140529-1~exp1 which
added the backlight helper.

Summary of what happened so far:

intel_backlight, which is default since Linux 3.16, does not work
correctly on several laptops. They have been blacklisted in the kernel
in order to use the working ACPI backlight again. #772440 is about just
another laptop model to be added to this blacklist.
Luca Boccassi found that the new backlight helper script in
xserver-xorg-video-intel also fixes the issue.



On 02/20/2015 12:29 AM, Luca Boccassi wrote:
> Cross-post from freedesktop bug, just to make sure it doesn't go unnoticed:
> 
> (In reply to Luca Boccassi from comment #13)
>> Hello,
>>
>> I have a Dell Latitude E5540, running an Intel Haswell i7-4600U with GPU HD
>> Graphics 4400, and I have the same problem. But I noticed that upgrading the
>> Intel driver to a version that ships a new backlight helper binary fixes the
>> problem.
>>
>> In my case, I am running Debian Jessie. The driver is part of the package
>> xserver-xorg-video-intel and the version that ships the new backlight
>> helper, according to the changelog, is:
>>
>> xserver-xorg-video-intel (2:2.99.911+git20140529-1~exp1) experimental;
>> urgency=low
>>
>>   * New upstream prerelease. (closes: #748753)
>>   * Install new backlight helper.

Confirmed, in
git://anonscm.debian.org/pkg-xorg/driver/xserver-xorg-video-intel I
found the new backlight helper script to be the relevant commit.

Also see the ongoing discussion in
https://bugs.freedesktop.org/show_bug.cgi?id=87286.

IMO the disable_native_backlight for some laptop models is (part of) the
correct solution and it is not clear /why/ the new backlight helper
script helps.

Should we clone this bug as a more general one and then reassign to
xserver-xorg-video-intel? We could then try to backport the changes to
jessie to also help other affected laptops which are not yet blacklisted.
That would be the following commits + probably some follow-up fixes. At
least the 3rd commit requires manual merging:

commit 631b4e4c78a807e61214026bf9a1461aadbd59b5
Author: maximilian attems <maks@***>
Date:   Thu May 29 17:07:16 2014 +0200
    install add new helper

commit b71f3d8bd4d6773899c1bdc903911cf240e68ead
Author: Jan Alexander Steffens (heftig) <jan.steffens@***>
Date:   Sat Feb 15 17:53:16 2014 +0100
    Backlight helper build fixes

commit 3d629c91cfa98b75c6685c2a2003e64fd1b612c4
Author: Chris Wilson <chris@***>
Date:   Sat Feb 15 14:55:09 2014 +0000
    intel: Add a helper for setting backlight without root rights

I just fear it is too late for that in jessie.

Greets
jre