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-   -   Backlight/Brightness control not working (http://www.nvnews.net/vbulletin/showthread.php?t=156880)

ThomasC 11-07-10 09:29 AM

Backlight/Brightness control not working
Hi Forum,

I write this thread because my backlight control auf my DELL Vostro 3700 doesn't work like it should do.

I can control it with the hardware keys FN+Up/Down... but this was most time a litte bit buggy - sometimes I have to set the backlight to the lowest value and than when I scale it up again its reacting first time or it react right (to make it complete bright)

But now I found, that I have to set


Option        "RegistryDwords"        "EnableBrightnessControl=1"
in Xorg.conf section of the driver, which I also did.

The main problem is, that I can not control the brightness per software with as example:

echo 0 | sudo tee /sys/devices/virtual/backlight/acpi_video0/brightness
echo 0 | sudo tee /sys/class/backlight/acpi_video0/brightness
echo 6 | sudo tee /proc/acpi/video/PEGP/LCD/brightness

None of them let the backlight react.

When I monitor all values with


watch -n1 "cat /sys/class/backlight/acpi_video0/brightness && cat /sys/devices/virtual/backlight/acpi_video0/brightness && cat /proc/acpi/video/PEGP/LCD/brightness"
and use the function keys to change the brightness I can see that all values get changed...

Any Idea what I can do?

I use Ubuntu Lucid Lynx with Nvidia driver 260.19.12 and kernel 2.6.36


XjCook 11-08-10 04:13 AM

Re: Backlight/Brightness control not working
Hi, you can try set backlight over hal:

first set

Option          "RegistryDwords" "EnableBrightnessControl=1"
in xorg.conf

then in file /usr/share/hal/fdi/information/10freedesktop/10-laptop-panel-hardware.fdi add this code:


<match key="/org/freedesktop/Hal/devices/computer:system.hardware.vendor" string="Sony Corporation">
  <match key="/org/freedesktop/Hal/devices/computer:system.hardware.product" contains_outof="VPCF11M1E">
          <merge key="laptop_panel.brightness_in_hardware" type="bool">false</merge>

Values of system.hardware.{vendor,product} you can detect with:

lshal | grep system.hardware.vendor
lshal | grep system.hardware.product

that's working for me :)

xificurk 12-27-10 05:43 PM

Re: Backlight/Brightness control not working
Hi, I have Dell Vostro 3700 too and I'm experiencing the same problem. I'm using Gentoo with latest stable kernel (2.6.36) and nvidia-drivers (260.19.29).

Furthermore I've tried nvidia-bl module provided by mactel, which was a partial success - I can control the brightness from command line via /sys/devices/virtual/backlight/nvidia_backlight/brightness. The remaining problem is that when I switch on/off compositing in KDE4, "something" resets the brightness level to the value that was set by Fn keys last time (my wild guess is that nvidia-driver remembers what was set by Fn keys and resets it).

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