[Ubuntu Wiki] Update of "Kernel/Debugging/Backlight" by brian-murray

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Tue Mar 1 16:25:10 UTC 2011


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The following page has been changed by brian-murray:
http://wiki.ubuntu.com/Kernel/Debugging/Backlight?action=diff&rev1=8&rev2=9

The comment on the change is:
reformat situations paragraph and add in thinkpad_apci info

------------------------------------------------------------------------------
  
  There are a lot of different issues with backlight control which can be generally put into these classes:
  
-  * Hotkeys change the brightness, but no OSD feedback and the brightness applet does not work. This normally is not a problem in Linux. If there is no vendor specific control mechanism and the generic ACPI interface is not defined (or not defined correctly), there is no way Linux can interact. In those cases the hotkeys are directly wired to the backlight control and no events are passed on to the OS.
+  * Hotkeys change the brightness, but no OSD feedback and the brightness applet does not work.
+   * There is nothing that the kernel can do to resolve this situation. Since there is no vendor specific control mechanism and the generic ACPI interface is not defined (or not defined correctly), there is no way Linux can interact. In those cases the hotkeys are directly wired to the backlight control and no events are passed on to the OS.
+  * Backlight control works through the brightness applet but not via hotkeys.
-  * Backlight control works through the brightness applet but not via hotkeys. This is most likely a hotkey issue which might be further debugged looking at [[https://wiki.ubuntu.com/Hotkeys/Troubleshooting|debugging hotkeys]].
+   * This is most likely a hotkey issue which might be further debugged looking at [[https://wiki.ubuntu.com/Hotkeys/Troubleshooting|debugging hotkeys]].
-  * Backlight control does not work, but there are entries in {{{/sys/class/backlight}}}. Might require the ACPI backlight driver to not take control to give a vendor specific driver a chance to register (see below).
+  * Backlight control does not work, but there are entries in {{{/sys/class/backlight}}}.
+   * This may require the ACPI backlight driver to not take control so that a vendor specific driver will have a chance to register (see below).
+  * Backlight control does not work and there are no entries in {{{/sys/class/backlight}}}.
-  * Backlight control does not work and there are no entries in {{{/sys/class/backlight}}}. Neither the ACPI backlight driver nor any vendor specific driver were able to find a valid interface. Either requires a new vendor driver (which is unlikely) or the ACPI BIOS is broken (see below). Updates to the ACPI BIOS are rare as well but in some cases it is possible to work with upstream to extend the Linux side to handle some of that brokenness.
+   * Neither the ACPI backlight driver nor any vendor specific driver were able to find a valid interface. Either requires a new vendor driver (which is unlikely) or the ACPI BIOS is broken (see below). Updates to the ACPI BIOS are rare as well but in some cases it is possible to work with upstream to extend the Linux side to handle some of that brokenness.
  
  = Filing Bugs =
  
@@ -32, +36 @@

  
  {{{
  thinkpad-acpi.brightness_enable=1
+ }}}
+ 
+ You can check to see if your system uses the '''thinkpad-acpi''' driver by using the following command:
+ 
+ {{{
+ lsmod | grep thinkpad_acpi
  }}}
  
  === Disabling ACPI brightness adjustments ===



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