Arch Linux

eto.renol

Member

Registered: 2011-07-31

Posts: 3

Screen back-light dimming

Hi,

I'm using Gnome-shell on my Dell Latitude E6420 and I'm experiencing a really annoying problem caused by the power management system. When  I try to dim the screen backlight using the keyboard, the system reacts only after several milliseconds (if not seconds) and also the mouse pointer gets very slow to respond.
Killing the gnome-power-manager daemon slightly improves the situation (the pointer is no longer affected by slowness), but the the screen back-light adjustment is always too slow.
Any idea?

Thanks in advance

marsark

Member

Registered: 2011-12-23

Posts: 2

Re: Screen back-light dimming

Hi, I have same problem as you described in Xfce desktop. The delay is about 2 seconds in my setup. I tried to some solution via dell_laptop module, but no luck

mrmylanman

Member

From: Altamonte Springs, FL, USA

Registered: 2011-03-13

Posts: 178

Re: Screen back-light dimming

I just set up manual keyboard shortcuts.

For example:

Go to Menu>Settings>Keyboard

Make two shortcuts:

xbacklight -dec 10% (map this one to XF86MonBrightnessDown)
xbacklight -inc 10% (map this one to XF86MonBrightnessUp)

This way you'll be able to manually change the brightness using the brightness keys, without the need for Gnome's power manager daemon.  Note that you can change the 10% to make the brightness adjustments more or less aggressive, depending on your personal taste.

Edit:

I should clarify, I'm using XFCE, not Gnome Shell.  You should still be able to generate these shortcuts in Gnome, however.  You'll lose the pretty onscreen notification that you changed the brightness, but I don't think that's necessarily bad.

Last edited by mrmylanman (2011-12-24 19:32:06)

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Arch user since 2011-03-13

Thinkpad X220 Intel Core i7-2640M CPU, 16GB DDR3-1333 RAM, 160GB Intel SATA II SSD & 60GB OCZ mSATA SSD, 12.5" IPS 1366x768 Display, 6-cell Battery
(Installation date:  2012-03-19)

jimbok

Member

Registered: 2009-09-17

Posts: 51

Re: Screen back-light dimming

Hmm, I just installed gnome and noticed that too.  It seemed to get better when I unchecked the disable touchpad when typing box. It's a laptop so I'll have to double check.

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Registered Linux User #402088

marsark

Member

Registered: 2011-12-23

Posts: 2

Re: Screen back-light dimming

So, I have found the cause of the problem and solved it. The problem is that there are two different drivers trying to control backlight PWM value. This leads to the collision. First driver is i915 and the second is apci. i915 is direct raw path via hw. Acpi path goes trough ACPI, BIOS and other crapy stuff. If this is your case, can be found in /sys.

In the /sys/class/backlight I have subdirs intel_backlight and acpi_video0, names may vary. You can try to set backlight PWM via file brightness (check max value in file max_brightness). In the case of ACPI path LCD backlight reaction is delayed by the 500 ms and the mouse cursor stuck for this time. Intel path acts immediately. 

I was able to disable acpi driver by adding option acpi_backlight=vendor to the kernel args. After reboot the acpi_video0 subdir is gone.