Brightness issues with Ubuntu Linux 12.04 on Samsung 700Z3A

[sarntam]

Hi everybody! I am currently setting up Ubuntu Linux 12.04 Precise Pangolin on my Samsung laptop/notebook 700Z3A. I added the PPA and installed samsung-tools and samsung-laptop through it. It got the light lensor for the keyboard backlight working, but the screen backlight remained troublesome. I added "acpi_backlight=vendor apci_osi=Linux" to my kernel command line in /etc/default/grub (and called update-grub and rebooted). I also patched /etc/X11/xorg.conf to include the line

Code: Select all

	Option "RegistryDwords" "EnableBrightnessControl=1"

in the section "Device".

With all the options above, backlight control still wasn't working. I tried installing samsung-backlight from the PPA, which actually worked, but only once. After rebooting it stopped working, and when I try to sudo modprobe it, it says "no such device". Adding the "force" parameter does no good either.

I am able to control the backlight via the command line tool xbacklight, and I wanted to use this potential to enable the FN keys manually. I edited ~/xbindkeysrc and added the lines

Code: Select all

"xbacklight -inc 20"
  XF86MonBrightnessUp
"xbacklight -dec 20"
  XF86MonBrightnessDown

And it worked! Well, sometimes it works and sometimes it doesn't. After I reboot my PC, I am consistently able to alter the backlight settings via the FN keys. However, sometimes (maybe after going to the standby mode several times? Or is it related to plugging the AC adapter in and out several times?) the system breaks and I can no longer use xbacklight to control the screen brightness. I then have to reboot.

How can I tell what is causing this random behaviour?

I use the proprietary Radeon catalyst driver to switch between the integrated Intel HD Graphics 3000 and the dedicated Radeon 6490M. These issues appear with both the Intel GPU and the AMD GPU.

[sarntam]

I have diagnosed this problem further:
whenever I reboot my computer the brightness control works flawlessly.
When I log out of Ubuntu and then back in (without restarting), the brightness goes haywire.

I don't know what that's connected to, I guess I will have to reboot every time I switch my graphics card.

[sarntam]

I fixed it! I needed to remove acpi_backlight=vendor from the GRUB Kernel command line. It now looks like this:

Code: Select all

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash pcie_aspm=force i915.i915_enable_rc6=1 i915.i915_enable_fbc=1 i915.lvds_downclock=1 acpi_osi=linux"

I no longer use the xbacklight solution (it gets overridden by Samsung-Tools anyway), but I still have the added line in xorg.conf.

[dokala]

This worked for me. I followed your steps except ~/.xbindkeysrc. I am on 12.10 Ubuntu / Samsung R480.

Thanks!

[david]

I fixed it! I needed to remove acpi_backlight=vendor from the GRUB Kernel command line. It now looks like this:

Code: Select all

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash pcie_aspm=force i915.i915_enable_rc6=1 i915.i915_enable_fbc=1 i915.lvds_downclock=1 acpi_osi=linux"

I no longer use the xbacklight solution (it gets overridden by Samsung-Tools anyway), but I still have the added line in xorg.conf.

I am not using Ubuntu but rather Puppy Linux dpup Exprimo.

What, please, is "Samsung-Tools"?

Is this something in BIOS or a Linux add-on?

Also, are the "915" references in your GRUB related to the screen brightness somehow or something else?

Thanks!