Arch Linux

Archimaredes

Member

Registered: 2013-01-23

Posts: 60

Weird issues changing backlight brightness on Dell Studio 1555

Hi,

I've found that GNOME's integrated control for backlight brightness doesn't function on this laptop, and the brightness control keys on the keyboard are very glitchy; they seem to flicker the brightness randomly instead of consistently raise and lower it, even though GNOME's icon with its bar appears on the screen properly. The control keys work when I'm not booted into Arch Linux.

My current kernel parameter set up is as follows:

quiet splash video.use_native_backlight=1

The video.use_native_backlight=1 parameter doesn't seem to make a difference though, and neither has acpi_backlight=vendor. I've also tried disabling the dell_laptop module to no effect.

I have two folders in /sys/class/backlight, dell_backlight and radeon_bl0. The Dell entry has a max_brightness of 15. Both the control keys and the integrated control change the brightness number, even though the integrated control doesn't change the brightness physically at all. Meanwhile, the radeon_bl0 brightness number (with a maximum of 255) doesn't change in response to control keys or the integrated control.

I'm using the open-source radeon driver. This laptop has a mobile ATI Radeon HD chip (4000 series).

Oh, and with my current setup, before GDM starts up (but after the kernel has booted), the control keys seem to switch the brightness between only 2 settings instead of a range, which seems to indicate my kernel parameters are indeed incorrect.

If anyone has experience using this laptop (or similar ones) and knows how to fix this issue I'd greatly appreciate it, because basically I can't change the brightness without hitting keys randomly until it looks vaguely right. Writing values to the 'brightness' file doesn't do anything either.

Last edited by Archimaredes (2015-05-23 15:33:59)

Archimaredes

Member

Registered: 2013-01-23

Posts: 60

Re: Weird issues changing backlight brightness on Dell Studio 1555

It might also be worth mentioning that a good few months ago when I had Arch Linux installed on this laptop with XFCE, the backlight brightness could be adjusted perfectly. This issue may be related to GNOME.

Archimaredes

Member

Registered: 2013-01-23

Posts: 60

Re: Weird issues changing backlight brightness on Dell Studio 1555

Bringing it up again...

ewaller

Administrator

From: Pasadena, CA

Registered: 2009-07-13

Posts: 20,655

Re: Weird issues changing backlight brightness on Dell Studio 1555

Well, the use native backlight switch is the general solution to this issue.

As a sanity check, what is the output of cat /proc/cmdline   ?

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Head_on_a_Stick

Member

From: The Wirral

Registered: 2014-02-20

Posts: 9,003

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Re: Weird issues changing backlight brightness on Dell Studio 1555

There are other kernel parameters you can try:

acpi_osi=!* acpi_osi="dell_laptop"
acpi_osi="dell_laptop" acpi_osi=!*

The first disables the "dell_laptop" module, the second enables it.

See here for more on this and for a complete listing of all kernel parameters:
https://www.kernel.org/doc/Documentatio … meters.txt

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