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+What: /sys/class/backlight/<backlight>/bl_power
+Date: April 2005
+KernelVersion: 2.6.12
+Contact: Richard Purdie <rpurdie@rpsys.net>
+Description:
+ Control BACKLIGHT power, values are FB_BLANK_* from fb.h
+
+ - FB_BLANK_UNBLANK (0) : power on.
+ - FB_BLANK_POWERDOWN (4) : power off
+Users: HAL
+
+What: /sys/class/backlight/<backlight>/brightness
+Date: April 2005
+KernelVersion: 2.6.12
+Contact: Richard Purdie <rpurdie@rpsys.net>
+Description:
+ Control the brightness for this <backlight>. Values
+ are between 0 and max_brightness. This file will also
+ show the brightness level stored in the driver, which
+ may not be the actual brightness (see actual_brightness).
+Users: HAL
+
+What: /sys/class/backlight/<backlight>/actual_brightness
+Date: March 2006
+KernelVersion: 2.6.17
+Contact: Richard Purdie <rpurdie@rpsys.net>
+Description:
+ Show the actual brightness by querying the hardware.
+Users: HAL
+
+What: /sys/class/backlight/<backlight>/max_brightness
+Date: April 2005
+KernelVersion: 2.6.12
+Contact: Richard Purdie <rpurdie@rpsys.net>
+Description:
+ Maximum brightness for <backlight>.
+Users: HAL
+
+What: /sys/class/backlight/<backlight>/type
+Date: September 2010
+KernelVersion: 2.6.37
+Contact: Matthew Garrett <mjg@redhat.com>
+Description:
+ The type of interface controlled by <backlight>.
+ "firmware": The driver uses a standard firmware interface
+ "platform": The driver uses a platform-specific interface
+ "raw": The driver controls hardware registers directly
+
+ In the general case, when multiple backlight
+ interfaces are available for a single device, firmware
+ control should be preferred to platform control should
+ be preferred to raw control. Using a firmware
+ interface reduces the probability of confusion with
+ the hardware and the OS independently updating the
+ backlight state. Platform interfaces are mostly a
+ holdover from pre-standardisation of firmware
+ interfaces.