Cannot change backlight brightness Ubuntu 14.04

[cyrus_the_virus]

This morning I found that I cannot change the brightness of my Dell XPs 13 laptop's display anymore. I tried the following to change the brightness

- Use keyboard brightness keys
- Run the commands shown below
- Boot with kernel option acpi_backlight=vendor. This resulted in a dell_something folder being present in the /sys/class/backlight folder. Changing the brightness file in that folder does not help.
- Add 'intel_backlight' to xorg.conf
- Set "load legacy option ROM" BIOS option to enabled and "secure boot" to disabled
- Boot with kernel option i915.disable-pch_pwm=0
- Boot from a fresh Ubuntu 12.04 USB stick installation. I can still not control the brightness. Maybe this a hardware problem?

Any ideas why this broke suddendly? I've upgraded from 12.04 to 14.04 in April and till yesterday the brightness keys were working fine.

echo 100 > /sys/class/backlight/intel_backlight/brightness
echo 100 > /sys/class/backlight/acpi_video0/brightness

Thanks!

[madvinegar]

Try getting into BIOS and change the "Load Legacy Option Rom" to "Enabled".

[cyrus_the_virus]

Thanks for your help. I've tried this but unfortunately it does not work for me. I did some more research and found this related bug report. It seems that this is a very common problem.

[jeremy31]

Cyrus, does the osd for brightness appear on your display when you try the brightness hotkeys? Do you get any resonse from terminal command

acpi_listen

[cyrus_the_virus]

Hi Jeremy,

Yes, the OSD brightness appears when I use the hotkeys. The acpi_listen command shows the following:

$ acpi_listen
video/brightnessup BRTUP 00000086 00000000
 PNP0C14:00 000000d0 00000000
video/brightnessup BRTUP 00000086 00000000
 PNP0C14:00 000000d0 00000000
video/brightnessdown BRTDN 00000087 00000000
 PNP0C14:00 000000d0 00000000
video/brightnessdown BRTDN 00000087 00000000
 PNP0C14:00 000000d0 00000000
video/brightnessdown BRTDN 00000087 00000000
 PNP0C14:00 000000d0 00000000

[jeremy31]

video.use_native_backlight=1

in grub without anything other than quiet splash

Your line in /etc/default/grub should be

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash video.use_native_backlight=1"

[cyrus_the_virus]

I have tried to do that (and run update-grub) but unfortunately it does not help

[jeremy31]

I have tried to do that (and run update-grub) but unfortunately it does not help

I am just wondering what is going on

cat /proc/cmdline

ls /sys/class/backlight

cat /var/log/Xorg.0.log | grep backlight

And what exactly did you do to add intel_backlight to xorg.conf? Where is the file at and what is it named and what does it contain?

Have you run Toz's handy script

for interface in /sys/class/backlight/*; do echo $interface; cat $interface/actual_brightness; cat $interface/max_brightness; done

[cyrus_the_virus]

I used this/ article that suggests making a change in xorg.conf. I removed this later because it does solve my problem. I think it just tells to which file the brightness value should be echoed, but since echoing a value manually does not work this solution does not work either.

Here is the output of the commands that you gave me:

$ cat /proc/cmdline
BOOT_IMAGE=/boot/vmlinuz-3.13.0-29-generic root=UUID=4e04ddb0-3020-4b02-827f-635306f670db ro quiet splash video.use_native_backlight=1 vt.handoff=7

$ ls /sys/class/backlight
intel_backlight

$ cat /var/log/Xorg.0.log | grep backlight
[    11.054] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-3.13.0-29-generic root=UUID=4e04ddb0-3020-4b02-827f-635306f670db ro quiet splash video.use_native_backlight=1 vt.handoff=7
[    11.101] (--) intel(0): found backlight control interface intel_backlight (type 'raw')

$ for interface in /sys/class/backlight/*; do echo $interface; cat $interface/actual_brightness; cat $interface/max_brightness; done
/sys/class/backlight/intel_backlight
4882
4882

Note that this was done with video.use_native_backlight=1

[cyrus_the_virus]

I used this/ article that suggests making a change in xorg.conf. I removed this later because it does solve my problem. I think it just tells to which file the brightness value should be echoed, but since echoing a value manually does not work this solution does not work either.

Here is the output of the commands that you gave me:

$ cat /proc/cmdline
BOOT_IMAGE=/boot/vmlinuz-3.13.0-29-generic root=UUID=4e04ddb0-3020-4b02-827f-635306f670db ro quiet splash video.use_native_backlight=1 vt.handoff=7

$ ls /sys/class/backlight
intel_backlight

$ cat /var/log/Xorg.0.log | grep backlight
[    11.054] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-3.13.0-29-generic root=UUID=4e04ddb0-3020-4b02-827f-635306f670db ro quiet splash video.use_native_backlight=1 vt.handoff=7
[    11.101] (--) intel(0): found backlight control interface intel_backlight (type 'raw')

$ for interface in /sys/class/backlight/*; do echo $interface; cat $interface/actual_brightness; cat $interface/max_brightness; done
/sys/class/backlight/intel_backlight
4882
4882

Note that this was done with video.use_native_backlight=1