Writing a laptop display backlight controller for Gnu \ Linux

Hello. Once, I wanted to build Gentoo on my Samsung n143 laptop. After a night of compilation, it came to building a graphical shell. I chose my usual KDE4, assembled, installed. All the hardware and Fn-keys worked perfectly except for the Fn-keys for adjusting the backlight level of the display (and software adjustment in the KDE System Settings). I tried to solve the problem by installing the samsung-backlight and samsug-tools packages, but nothing happened.
Those who are interested in how I solved this problem, please under the cat.

A little googling found a way to adjust the backlight through «setpci». To do this, you must first obtain the entire list of PCI devices using lspci, find the “address” of the device we need and set the desired value.

# lspci 00:00.0 Host bridge: Intel Corporation Mobile 4 Series Chipset Memory Controller Hub (rev 07) 00:02.0 VGA compatible controller: Intel Corporation Mobile 4 Series Chipset Integrated Graphics Controller (rev 07) 00:02.1 Display controller: Intel Corporation Mobile 4 Series Chipset Integrated Graphics Controller (rev 07) 00:1a.0 USB Controller: Intel Corporation 82801I (ICH9 Family) USB UHCI Controller #4 (rev 03) 00:1a.1 USB Controller: Intel Corporation 82801I (ICH9 Family) USB UHCI Controller #5 (rev 03) 00:1a.2 USB Controller: Intel Corporation 82801I (ICH9 Family) USB UHCI Controller #6 (rev 03) 00:1a.7 USB Controller: Intel Corporation 82801I (ICH9 Family) USB2 EHCI Controller #2 (rev 03) 00:1b.0 Audio device: Intel Corporation 82801I (ICH9 Family) HD Audio Controller (rev 03) 00:1c.0 PCI bridge: Intel Corporation 82801I (ICH9 Family) PCI Express Port 1 (rev 03) 00:1c.2 PCI bridge: Intel Corporation 82801I (ICH9 Family) PCI Express Port 3 (rev 03) 00:1c.3 PCI bridge: Intel Corporation 82801I (ICH9 Family) PCI Express Port 4 (rev 03) 00:1d.0 USB Controller: Intel Corporation 82801I (ICH9 Family) USB UHCI Controller #1 (rev 03) 00:1d.1 USB Controller: Intel Corporation 82801I (ICH9 Family) USB UHCI Controller #2 (rev 03) 00:1d.2 USB Controller: Intel Corporation 82801I (ICH9 Family) USB UHCI Controller #3 (rev 03) 00:1d.7 USB Controller: Intel Corporation 82801I (ICH9 Family) USB2 EHCI Controller #1 (rev 03) 00:1e.0 PCI bridge: Intel Corporation 82801 Mobile PCI Bridge (rev 93) 00:1f.0 ISA bridge: Intel Corporation ICH9M LPC Interface Controller (rev 03) 00:1f.2 SATA controller: Intel Corporation ICH9M/ME SATA AHCI Controller (rev 03) 00:1f.3 SMBus: Intel Corporation 82801I (ICH9 Family) SMBus Controller (rev 03) 02:00.0 Ethernet controller: Atheros Communications Inc. AR242x / AR542x Wireless Network Adapter (PCI-Express) (rev 01) 06:00.0 Ethernet controller: Marvell Technology Group Ltd. 88E8057 PCI-E Gigabit Ethernet Controller (rev 10) 

In my case, the “necessary” device is “00: 02.0 VGA compatible controller: Intel Corporation Mobile 4 Series Chipset Integrated Graphics Controller (rev 07)”. To configure pci devices, you can use the “setpci” utilities.
Requires root to execute:

 # setpci -s 00:02.0 F4.B=<VALUE> 

Where

• VALUE - the value of the backlight level in HEX (00..FF)
• The s - key allows you to specify the device in the following format: "[[[[]:]]:][][.[] ]".
-d []:[] ( lspci "-n")


! , . : Hot-Key-. C, \ " " .

:
"[[[[]:]]:][][.[] ]".
-d []:[] ( lspci "-n")


! , . : Hot-Key-. C, \ " " .

:


   #include <stdio.h> #include <stdlib.h> #define DEVICEPATH "/sys/devices/pci0000:00/0000:00:02.0/config" //   #define STEP 10 //     int getLevel(void) { int current_level = -1; FILE *device_file = 0; device_file = fopen(DEVICEPATH,"rb"); if( 0 != device_file) { if( 0 == fseek(device_file,244,0) ) { current_level = fgetc(device_file); fclose(device_file); } } return current_level; } int ChangeLevel(const int value) { int functionResult = -1; if( (value > -1) && (value < 256) ) { FILE *device_file = 0; device_file = fopen(DEVICEPATH,"r+b"); if( 0 != device_file ) { if( 0 == fseek(device_file,244,0) ) { fputc(value,device_file); fclose(device_file); functionResult = 0; } } } else { printf("Error! Incorrect input value. Try 0..255\n"); } return functionResult; } int main(int argc, char * argv[]) { int current_level = 0; if( argc > 1 && argc < 3 ) { if( -1 != (current_level=getLevel()) ) { switch( *argv[1] ) { case 'u': if( current_level < ( 255 - STEP ) ) { if( -1 != ChangeLevel( current_level + STEP ) ) { printf("Ok, done\n"); } } else { printf("Error setting level\n"); } break; case 'd': if( current_level > (0+STEP) ) { if( -1 != ChangeLevel(current_level-STEP) ) { printf("Ok, done\n"); } } else { printf("Error setting level\n"); } break; case 'c' : printf("Current brightness level: %d\n",current_level); break; case 's': ChangeLevel(atoi(argv[2])); break; default: printf("Invalid arguments\n"); break; } } else { printf("Error checking brightness level\n"); } } else { printf("Arguments: [u|d|c|s <0..255>]\n"); printf("Usage:\nu - increase brightness by STEP value\n"); printf("d - decrease by STEP\n"); printf("c - show current level\n"); printf("s - set brightness to value 0..255.\n 0 - backlight off | 255 - maximum level\n"); } return 0; } 

  
  
  Compile the code:
  

   gcc main.c -o bcontroller 

  
  Set root permissions:
  

   chown root:root bcontroller chmod +s bcontroller 

  
  Copy the program to bin:
  

   cp ./bcontroller /usr/bin/bcontroller 

  
  As can be seen from the source code, the application can be called with different parameters:
  
  • u - Increase the backlight level by 1 step
  • d - Reduce the backlight level by 1 step.
  • s - Set the value of the backlight level in the range 0..255
  • c - View current backlight level
  
  After we have copied the program to / usr / bin, we will tie it to the hotkeys in KDE4. Go to the system settings -> Actions, or Options -> Keyboard and Mouse -> Keyboard Shortcuts (or Basic Actions). Select the component that is responsible for adjusting the backlight, select the effect of increasing the backlight level and enter the command: bcontroller u . Similarly, you can add to reduce, turn off / on the backlight. In GNOME, you can do all this through System -> Preferences -> Keyboard Shortcuts -> Add. In the pop-up menu, add a command and hotkeys.
  Thanks for attention!
  
  PS Thanks for correcting the error, newdya