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#1 2012-10-15 15:00:57

bfreonix
Member
Registered: 2011-07-19
Posts: 4

Dell XPS 13 Ultrabook L321X brightness control

I wasn't able to get the brightness working. So far I've tried:
1. Controlling via /sys/class/backlight/acpi_video0
- max brightness was 15
- does not respond to "echo 5 > /sys/class/backlight/acpi_video0/brightness"
- "cat /sys/class/backlight/acpi_video0/actual_brightness" shows 5 but have no effect

2. Controlling via /sys/class/backlight/intel_backlight
- changing the brightness value will result in screen flicker
- have to max it out to get rid of the flicker

Does anyone have arch working on this model? I'm lost.

Last edited by bfreonix (2012-10-15 15:03:23)

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#2 2012-10-26 17:53:23

aprescott
Member
Registered: 2012-07-07
Posts: 7

Re: Dell XPS 13 Ultrabook L321X brightness control

Did you ever get anywhere with this issue? I'd love a fix.

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#3 2012-10-28 02:58:01

EGriffith92
Member
Registered: 2012-01-25
Posts: 6

Re: Dell XPS 13 Ultrabook L321X brightness control

Guys can one or both of you install:

https://aur.archlinux.org/packages.php?ID=60736

Ive also an XPS ultrabook and im wanting to see if that package fixes the backlight issues before I jump to Arch on this.

Warning: That package does pull in 3.7rc-1, which is a pre-release kernel. So you may get a kernel oops/panic/other bugs when running that kernel. But do me (and all others) a favor and run that with the standard backlight and intel_backlight and see if either one gets you a stable backlight

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#4 2012-11-16 04:17:46

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

Re: Dell XPS 13 Ultrabook L321X brightness control

I've got a fix working for my XPS 13 (although I'm struggling to get it working at boot with systemd currently).

Anyways, through trial and error I've found that I need to set /sys/class/backlight/intel_backlight/brightness to 0 before changes to /sys/class/backlight/acpi_video0/brightness will affect actual screen brightness. You will need to do this regardless of whether the intel_backlight/brightness is already set to zero, the act of setting the value is what allows the acpi_video0 interface to change the brightness.

I use this script after login to initialize my ability to modify screen brightness:

#!/bin/bash

# set intel interface to 0, allowing acpi interface to take precedence
echo 0 > /sys/class/backlight/intel_backlight/brightness

# set the permissions of the acpi brightness file for convenience of non-root modification
# (works if user is a member of the video group)
chgrp video /sys/class/backlight/acpi_video0/brightness
chmod 664 /sys/class/backlight/acpi_video0/brightness

# initialize brightness to a low level
echo 3 > /sys/class/backlight/acpi_video0/brightness

exit 0

I don't really understand the underlying reasons as to why the intel_backlight needs to be zeroed, if anyone knows please post.

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#5 2012-11-16 14:52:05

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

Re: Dell XPS 13 Ultrabook L321X brightness control

In regards to the patched kernel...

I installed that last night and it doesn't magically fix brightness and touchpad issues. I need to see if its a problem with something else before I can claim that the patched kernel is useless, I'll report back if I can get it to work.

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#6 2012-12-21 19:23:42

aprescott
Member
Registered: 2012-07-07
Posts: 7

Re: Dell XPS 13 Ultrabook L321X brightness control

tyler.heck wrote:

Anyways, through trial and error I've found that I need to set /sys/class/backlight/intel_backlight/brightness to 0 before changes to /sys/class/backlight/acpi_video0/brightness will affect actual screen brightness. You will need to do this regardless of whether the intel_backlight/brightness is already set to zero, the act of setting the value is what allows the acpi_video0 interface to change the brightness.

I use this script after login to initialize my ability to modify screen brightness:

I can confirm this enables brightness control, both through the GUI systems settings and the Function shortcut on the keyboard. I have no idea how you did it, but thank you!

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#7 2013-01-22 01:57:46

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

Re: Dell XPS 13 Ultrabook L321X brightness control

Finally, I figured out a way to start the script as a systemd service and put it up here: https://bbs.archlinux.org/viewtopic.php?id=156219 . It's another workaround, but it works and I could never find a nice way to do it.

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#8 2013-01-22 04:30:26

gsgleason
Member
Registered: 2012-10-08
Posts: 59

Re: Dell XPS 13 Ultrabook L321X brightness control

I had an XPS 15 and what I found was that adding the following kernel parameters broke it and caused what you have:

acpi_osi=Linux acpi_backlight=vendor

Before I added those, the hotkeys worked, and I could see /sys/class/backlight/acpi_video1 was being updated as I used the hotkeys, and I could read the brightness as well.  Removing those paramters fixed it for me on the XPS 15.

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