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#1 2013-02-08 22:18:20

AurosGamma
Member
From: San Cristobal,Venezuela
Registered: 2011-02-22
Posts: 132

Screen Brightness only changeable through /sys/class/intel_backlight

I have an ASUS N56VZ-DS71 with Optimus, it comes with an Intel HD Graphics 4000 and nVidia Geforce GT 650M. I installed KDE 4.10 today and I cannot change the screen brightness using the FN+F{5,6} keys nor using the KDE power management tool slider. However, I can do change the screen brightness echoing to

/sys/class/backlight/intel_backlight/brightness

In the same "backlight" folder, there are another interfaces present apart from "intel_backlight"

/sys/class/backlight/acpi_video0
/sys/class/backlight/acpi_video1
/sys/class/backlight/intel_backlight

I've read though the internet and found that KDE chooses between the interfaces depending on the type of each one (firmware, platform or raw) in that order. The types of each interface is:

/sys/class/backlight/acpi_video0 = firmware
/sys/class/backlight/acpi_video1 = firmware
/sys/class/backlight/intel_backlight = raw

But since, KDE chooses firmware type over raw, intel_backlight is never chosen. I've tried adding "acpi_backlight=vendor" to the kernel parameters. After rebooting the content of the "/sys/class/backlight" folder changed, with the two acpi_video{0,1} interfaces removed, and a new one added:

/sys/class/backlight/asus-nb-wmi = platform
/sys/class/backlight/intel_backlight = raw

But the problem still persist, because KDE stills chooses platform type over raw (echoing to /sys/class/backlight/asus-nb-wmi/brightness doesn't work neither).

So I'm asking,  there's fix for this problem? Because looks like the other interfaces are ignored, intel_backlight is the only one that works.

Cheers

Last edited by AurosGamma (2013-02-08 22:20:03)

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#2 2013-02-08 22:29:00

jasonwryan
Anarchist
From: .nz
Registered: 2009-05-09
Posts: 20,078
Website

Re: Screen Brightness only changeable through /sys/class/intel_backlight

Write a simple script and bind it to the relevant key(s)...


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#3 2013-02-08 22:39:27

AurosGamma
Member
From: San Cristobal,Venezuela
Registered: 2011-02-22
Posts: 132

Re: Screen Brightness only changeable through /sys/class/intel_backlight

Seems to be the best solution until a fix comes out. But I wonder, is this a KDE problem or Linux problem? Because I could try to help fixing it.

Note: I forgot to mention that I had no problems before the fresh install, I was able to change the brightness through KDE Power Manager panel, maybe a recent kernel update messed up something?

Last edited by AurosGamma (2013-02-08 22:47:02)

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#4 2013-02-08 22:42:14

jasonwryan
Anarchist
From: .nz
Registered: 2009-05-09
Posts: 20,078
Website

Re: Screen Brightness only changeable through /sys/class/intel_backlight

There have been a lot of posts about this issue since 3.7: presumably it will get ironed out in a future release...


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#5 2013-02-08 22:49:36

AurosGamma
Member
From: San Cristobal,Venezuela
Registered: 2011-02-22
Posts: 132

Re: Screen Brightness only changeable through /sys/class/intel_backlight

I'll try to boot using a previous Kernel Version and post some feedback.

Edit: Confirmed, the backlight can be changed as before using the Kernel 3.6.11, waiting for an upstream fix I guess.

Last edited by AurosGamma (2013-02-09 21:57:12)

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#6 2013-02-12 09:12:26

marno11
Member
Registered: 2011-05-25
Posts: 22

Re: Screen Brightness only changeable through /sys/class/intel_backlight

Hmmm, I'm having the same problem. I recently picked up an old Acer Aspire S3 ultrabook, I'm using a freash install of arch with xfce4 and I havent been able to get the xfce4-brightness-plugin to work.

Changing the appropiate values in /sys/class/backlight/acpi_video0/ (which is what the plugin does aswell) does nothing, but I can adjust brighness by changing the appropiate values in /sys/class/backlight/intel_backlight/ (though I must be logged in as root, sudo does not work)

Even after speding a fair ammount of time on this, I'm actualy not too clear how this is all ment to work? can someone explain or point me to an explination please?, whats the diffence between acpi_video0 and intel_backlight? when would you actually use one over the other?

as per the wiki i have tried adding these entries to grub (into the quotation marks of GRUB_CMDLINE_LINUX="")

acpi_osi=Linux acpi_backlight=vendor

and

acpi_osi=Linux acpi_backlight=legacy

and rebooting, but no luck

Last edited by marno11 (2013-02-12 09:17:07)

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#7 2013-02-22 15:39:10

egestatem
Member
Registered: 2013-02-22
Posts: 2

Re: Screen Brightness only changeable through /sys/class/intel_backlight

so what would be the relevant scripts? I tried putting a script in rc5.d to give users permission to edit this /sys/class/intel_backlight file, as it seems to be newly created each reboot, but it doesn't seem to hold. how can you bind the Fn+{F5, F6} keys to change this file as root? Am I missing something?

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#8 2013-02-22 15:56:52

WonderWoofy
Member
From: Los Gatos, CA
Registered: 2012-05-19
Posts: 8,412

Re: Screen Brightness only changeable through /sys/class/intel_backlight

Are you still using initscripts/SysV? I really am nit entirely sure if it is related, but you should probably read the news on the front page every once in a while.

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#9 2013-02-22 16:31:55

egestatem
Member
Registered: 2013-02-22
Posts: 2

Re: Screen Brightness only changeable through /sys/class/intel_backlight

WonderWoofy wrote:

Are you still using initscripts/SysV? I really am nit entirely sure if it is related, but you should probably read the news on the front page every once in a while.


oops, I'm using Linux Mint forgot this mattered. I have tried ubunt/mint forums for this issue, but this post has been the most relevant to my problem so far.

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#10 2013-02-22 16:39:37

ewaller
Administrator
From: Pasadena, CA
Registered: 2009-07-13
Posts: 13,805

Re: Screen Brightness only changeable through /sys/class/intel_backlight

egestatem wrote:

oops, I'm using Linux Mint forgot this mattered. I have tried ubunt/mint forums for this issue, but this post has been the most relevant to my problem so far.

First, welcome to ArchLinux.  Now for the scolding;  Please read our policy on support of non-Arch distributions and, to a lesser degree, thread highjacking

You are welcome here, but please, don't ask for support of Mint; it is a different animal.  Full disclosure when posting is a must.

Last edited by ewaller (2013-02-22 16:39:51)


Nothing is too wonderful to be true, if it be consistent with the laws of nature -- Michael Faraday
You assume people are rational and influenced by evidence.  You must not work with the public much. -- Trilby
----
How to Ask Questions the Smart Way

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#11 2013-02-22 16:41:26

WonderWoofy
Member
From: Los Gatos, CA
Registered: 2012-05-19
Posts: 8,412

Re: Screen Brightness only changeable through /sys/class/intel_backlight

@egastatem - Yeah, this is not going to be very relevant though because we are on different kernel versions.  You need to go to the forums of your own distribution for help.  Often times, you can read through these threads and find relevant info about various software that is used as well in other distros.  But you are now asking about a system with not only a different kernel version, but also an entirely different init system. 

Also, it would have been nice if you had been forthcoming with this information from your first post, as this time spent (though not much) has been wasted. 

These forums are for Arch Linux support only.


Edit: ewaller is quick... I am slow sad

Last edited by WonderWoofy (2013-02-22 16:42:16)

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