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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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Did you ever get anywhere with this issue? I'd love a fix.
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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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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 0I 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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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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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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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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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=vendorBefore 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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