[Ubuntu Wiki] Update of "Kernel/Debugging/Backlight" by penalvch

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Mon May 28 19:35:00 UTC 2018


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The "Kernel/Debugging/Backlight" page has been changed by penalvch:
http://wiki.ubuntu.com/Kernel/Debugging/Backlight?action=diff&rev1=35&rev2=36

Comment:
1) Minor presentation fixes. 2) MV link as overlap /w prior instructions.

   * Also, depending on the class of issues, provide additional information about the kernel interface. Does it exist, do any values change when writing into the control files? Is there any effect?
   * If the kernel interface does not work, add the dump of the ACPI BIOS as described below.
  
- = Debugging information to provide in your bug report =
+ = Information to provide in your bug report =
+  
+ == Debugging information ==
  
-  * Please file backlight bugs by executing at the Terminal: <<BR>> {{{ubuntu-bug linux}}} <<BR>> <<BR>> If it turns out to be a non-linux package issue, it can be changed to the appropriate package.
-  * Install the prerequisites by executing at the Terminal: <<BR>> {{{sudo apt-get install -y acpidump fwts dmidecode iasl}}}
+  * Please file backlight bugs by executing at a terminal:{{{
+ ubuntu-bug linux
+ }}} If it turns out to be a non-linux package issue, it can be changed to the appropriate package.
+  * Install the prerequisites by executing at a terminal:{{{
+ sudo apt-get install -y acpidump fwts dmidecode iasl}}}
   * Execute at a terminal each of the following in order, with default Ubuntu kernel parameters, and post the result of each command as a separate, non-compressed attachment to your report:
    * {{{ls /sys/class/backlight > backlight}}}
    * {{{grep -r . /proc/acpi > acpi}}}
@@ -39, +44 @@

  
  == Testing for a work around ==
  
+  The purpose of this section is to provide kernel developers further insight into what is causing your backlight to not work.
+ 
-  * Reboot with only the [[https://wiki.ubuntu.com/Kernel/KernelBootParameters|kernel parameter]] acpi_backlight=vendor :
+  * Boot with only the [[https://wiki.ubuntu.com/Kernel/KernelBootParameters|kernel parameter]]:{{{
+ acpi_backlight=vendor}}}
    * Make a comment on if you can now alter the backlight with hotkeys or a brightness applet.
+   * If you have the folder /sys/class/backlight/intel_backlight/ execute all of the following: {{{
-   * {{{ls /sys/class/backlight > vendorbacklight}}}
+ ls /sys/class/backlight > vendorbacklight
+ sudo su
-   * If you have the folder /sys/class/backlight/intel_backlight/ :
-    * type {{{sudo su}}} , and then execute:
-    * ls -la /sys/class/backlight/intel_backlight/ > lslabacklight
+ ls -la /sys/class/backlight/intel_backlight/ > lslabacklight
-    * {{{echo 8 > /sys/class/backlight/intel_backlight/brightness}}}
+ echo 8 > /sys/class/backlight/intel_backlight/brightness}}}
-     * Please comment on if the brightness changes.
+     * Please comment on if the brightness changes, and attach lslabacklight to your report.
+  * Boot with only the kernel parameter:{{{
-  * Reboot with just kernel parameter video.use_bios_initial_backlight=0 and make a comment on if you can now alter the backlight with hotkeys or a brightness applet.
+ video.use_bios_initial_backlight=0}}} and make a comment on if you can now alter the backlight with hotkeys or a brightness applet.
+  * Boot with only the kernel parameter:{{{
-  * Reboot with just kernel parameter acpi_osi= and make a comment on if you can now alter the backlight with hotkeys or a brightness applet.
+ acpi_osi=}}} and make a comment on if you can now alter the backlight with hotkeys or a brightness applet.
+  * Boot with only the kernel parameter:{{{
-  * If using a v3.13.x+ series kernel, reboot with just kernel parameter video.use_native_backlight=1 and make a comment on if you can now alter the backlight with hotkeys or a brightness applet.
+ video.use_native_backlight=1}}} and make a comment on if you can now alter the backlight with hotkeys or a brightness applet.
+  * If your backlight hotkeys are Fn+Left and Fn+Right, add kernel parameter{{{
-  * If your backlight hotkeys are Fn+Left and Fn+Right, add kernel parameter atkbd.softraw=0 to /boot/grub/menu.lst . Then, switch to any console, e.g. Ctrl+Alt+F1, login by root account and execute:<<BR>> {{{showkey -s}}} <<BR>> <<BR>> Then, press Fn+Left and Fn+Right key to check the code that shows up on screen. Post the results to the report. For example: <<BR>> <<BR>> Fn+Left: <<BR>> 0xe0 0x4c 0xe0 0xcc <<BR>> <<BR>> Fn+Right: <<BR>> 0xe0 0x54 0xe0 0xd4
+ atkbd.softraw=0}}} Then, switch to a console, e.g. Ctrl+Alt+F1, login by root account and execute:<<BR>> {{{showkey -s}}} <<BR>> <<BR>> Then, press Fn+Left and Fn+Right key to check the code that shows up on screen. Post the results to the report. For example: <<BR>> <<BR>> Fn+Left: <<BR>> 0xe0 0x4c 0xe0 0xcc <<BR>> <<BR>> Fn+Right: <<BR>> 0xe0 0x54 0xe0 0xd4
- 
- 
- 
- SEE ALSO:  [[https://help.ubuntu.com/community/ScreenBacklight|ScreenBacklight]]
- 
- 
  
  === Intel HD Graphic Controllers ===
  
@@ -237, +243 @@

  Reading the method definitions requires some knowledge about the ACPI AML language and some persistence on hunting down more or less complex implementations. Some are more obvious than others. There have been cases where percentage values got converted into index values and then (incorrectly) back on query.
  
  Also often the values get stored into a register of the embedded controller which does not necessarily need to have any result on the brightness.
+ 
+ = See also =
+ 
+  [[https://help.ubuntu.com/community/ScreenBacklight|ScreenBacklight]]
+ 
  ----
  CategoryDebugging
  



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