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#1 2013-01-13 08:54:41

Fluxis
Member
Registered: 2012-04-12
Posts: 5

Can not change backlight with /sys/class/backlight/acpi_video0

I am not able to change the brightness of the screen backlight with /sys/class/backlight/acpi_video0. actual_brightness and brightness both return 0 but the backlight is actually at full brightness.

I have tried passing acpi_osi=Linux acpi_backlight=vendor to linux but in that case /sys/class/backlight is empty.

After reading http://mjg59.livejournal.com/127103.html I am left with the impression that either I need a vendor module that does not exist or I should control the brightness via the GPU. The machine is a HP Pavilion DM1-4341 with a built in AMD Radeon HD 7340 Discrete-Class. I'm currently using the open source driver.

Does anyone have any suggestions?

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#2 2013-01-15 17:16:28

tyler.heck
Member
Registered: 2012-01-28
Posts: 15

Re: Can not change backlight with /sys/class/backlight/acpi_video0

I found that I first need to set the brightness of my graphics card interface to 0 before any changes to the acpi_video0 interface have any effect. In my case I alter the brightness file found in /sys/class/backlight/intel_backlight, which I assume corresponds to the Intel 3000 graphics card I have in my notebook.

Running following commands lets me change my screen brightness to a value x out of 15.:

 # echo 0 > /sys/class/backlight/intel_backlight/brightness
 # echo x > /sys/class/backlight/acpi_video0/brightness

I would try setting the brightness of your specific GPU interface to 0 before modifying the acpi_video0 brightness, hopefully the solution can be applied in general.

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#3 2013-01-15 19:48:42

Fluxis
Member
Registered: 2012-04-12
Posts: 5

Re: Can not change backlight with /sys/class/backlight/acpi_video0

Thank you for the response. I forgot to mention I only have acpi_video0 in my /sys/class/backlight/ directory. I will have to look into why the GPU brightness is not being registered.

Last edited by Fluxis (2013-01-15 19:49:04)

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