Edit (additional info)

Where do the 3 steps for 1 keypress come from?

You get three brightness steps for one keypress because:

1. The standard ACPI/video driver adjusts step 1


2. The thinkpad_acpi driver tells the BIOS to adjust step 2 but still forwards the keypress event


3. The GNOME power daemon intercepts this keypress and tells ACPI to adjust once again step 3

1. Disable the video driver from adjusting brightness on its own

This gets rid of one of the three steps (step 1) above.

• Open the terminal


• Type sudo sh -c 'echo -n 0 > /sys/module/video/parameters/brightness_switch_enabled'


• Test, now you should have brightness control in steps of two



• To automatically disable this on startup, open /etc/rc.local in your favorite editor, and before the last line (exit 0), add:

  
  
  

  echo -n 0 > /sys/module/video/parameters/brightness_switch_enabled

2. Recompile the thinkpad_acpi module to solve the double-press issue

• We have to stop thinkpad_acpi from adjusting the brightness via BIOS and have it only forward the keypress to GNOME, so that GNOME makes the only adjustment step


• This is a known bug which was fixed in kernel 3.4+



• To fix it for Ubuntu 12.04/Precise, we'll have patch its version of thinkpad_acpi and recompile it:

  
  
  
  
  
  1. Install the kernel headers: sudo apt-get install linux-headers-$(uname -r)
  
  
  2. Install build tools sudo apt-get install build-essential
  
  
  3. Make a temporary directory and change to it:
     

     mkdir ~/tpacpi-bright && cd ~/tpacpi-bright

  
  

  4. Download and patch the source file thinkpad_acpi.c from the Ubuntu Kernel git repository:

     
     
     

     wget -O- "http://kernel.ubuntu.com/git?p=ubuntu/ubuntu-precise.git;
     
     a=blob_plain;f=drivers/platform/x86/thinkpad_acpi.c;hb=HEAD"
     
     | sed -e 's/tp_features.bright_acpimode && acpi_video/acpi_video/g' 
     
     > thinkpad_acpi.c

  
  

  5. In the same folder where thinkpad_acpi.c has been downloaded, you will need a "Makefile". You can download it directly from this Pastebin, using:

     
     
     

     wget -OMakefile http://pastebin.com/raw.php?i=ybpnxeUT

  
  
  
  
  

  OR paste the below into a file called Makefile, :

  
  
  

  
  
  obj-m += thinkpad_acpi.o
  
  
  all:
  
  	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
  
  
  clean:
  
  	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
  
  

  
  
  
  
  
  1. Now type make to create the module; you will see a thinkpad_acpi.ko file in the folder when done.
  
  



• Test the patched module after loading it with:

  
  
  

  sudo rmmod thinkpad_acpi && sudo lsmod thinkpad_acpi.ko




• If the brightness is now fixed and gives you full control, replace the stock module with the patched module:

  
  
  

  
  
  TPDIR=/lib/modules/$(uname -r)/kernel/drivers/platform/x86
  
  sudo mv $TPDIR/thinkpad_acpi.ko $TPDIR/thinkpad_acpi.ko.stock
  
  sudo mv ~/tpacpi-bright/thinkpad_acpi.ko $TPDIR/thinkpad_acpi.ko
  
  




• You can clean up the build folder with make clean; keep it around for future kernel upgrades!