Bug 48681

Summary:	Brightness controls on Dell Latitude E6530 broken
Product:	ACPI	Reporter:	Martin Wildam (mwildam)
Component:	Power-Video	Assignee:	Aaron Lu (aaron.lu)
Status:	CLOSED INVALID
Severity:	normal	CC:	aaron.lu, e-mail
Priority:	P1
Hardware:	All
OS:	Linux
Kernel Version:		Subsystem:
Regression:	No	Bisected commit-id:
Attachments:	Logs (Kernel 3.4) Logs (Kernel 3.5)

Description Martin Wildam 2012-10-10 19:05:11 UTC

Created attachment 82821 [details]
Logs (Kernel 3.4)

It looks, I am experiencing a similar problem to bug 47861 (https://bugzilla.kernel.org/show_bug.cgi?id=47861)

I first experienced the problem on later kernels, but now also do experience the problem on kernel 3.4 - however, it already worked with 3.4. After several tests - sometimes I have this problem after boot and sometimes not. In my case it is not the Fn + F7 and F8 (as in the other bug), but Fn + Cursor up and down that should do the brightness regulation and do not work.

Interestingly in my case Fn + F1 (Put to suspend) works.

So somehow it seems not to be the keyboard the problem.

Another interesting thing I can observe: When I plugin the power cord to my laptop the screen dims and gets brighter again when I plug it off. This is the opposite effect that usually should be (being that while on power the screen is brighter as on battery).

Comment 1 Martin Wildam 2012-10-10 22:04:21 UTC

Neither kernel 3.4 nor kernel 3.6 brings back the functionality.

Comment 2 Igor Murzov 2012-10-13 00:59:13 UTC

I can't see from the logs how this bug is related to bug 47861.
If this bug is a regression, then I would recommend you to bisect it and find out the first commit that broke brightness controls on your laptop.

Comment 3 Martin Wildam 2012-10-24 20:33:10 UTC

From current point of view I think it has to do with ambient light sensor.

I examined BIOS and there is are two settings: For brightness on AC and for brightness on battery - in both cases it says "if ambient light sensor is off"

Sometimes I get those settings without brightness controls working. It looks like that in bright light the controls work but when it's quite dark, they do not and then the brightness controls are not working. Unfortunately I don't have an idea, where the sensor exactly is so that I can test it by putting my finger on it or hold a flashlight onto it.

Comment 4 Martin Wildam 2013-02-21 07:57:31 UTC

@Igor: Sorry, I am not into the kernel source code and so I cannot find the first commit that broke those controls - but maybe this is helping you:
https://launchpad.net/~kamalmostafa/+archive/linux-kamal-mjgbacklight
I am on Ubuntu 12.04 experiencing the problems so I assume that some fix has disappeared again later.

I am now on kernel 3.5.0-25-generic #38-Ubuntu since yesterday and tested brightness controls again right now. Interestingly now, if I press the Fn+Up or Fn+Down there is a delay of about 10 seconds and then I can see the bubble window popping up showing the brightness status and it is working.

Comment 5 Martin Wildam 2013-02-21 07:58:39 UTC

Created attachment 93781 [details]
Logs (Kernel 3.5)

Here are the logs for the test adjusting brightness doing it after about 10 seconds delay.

Comment 6 Martin Wildam 2013-02-21 08:33:45 UTC

Finally I found this article that solved my issue:
http://www.techjail.net/solved-brightness-problem-in-ubuntu-12-04-precise-pangolin.html

I had to add
    acpi_backlight=vendor
to my setting GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub
and do sudo update-grub

Now the brightness keys work in an instant.

Comment 7 Aaron Lu 2013-03-04 06:30:40 UTC

Hi Martin,

I don't think Fn+Cursor up/down can do brightness change in a standard way, unless your keyboard controller would generate the same scancode for these two keys as Fn+F7/F8, which is not likely.

So please keep using the vendor driver, that should be able to map those keys to brightness controls for you.