Merge tag 'backlight-next-5.4' of git://git.kernel.org/pub/scm/linux/kernel/git/lee/backlight

Pull backlight updates from Lee Jones:
 "Core Frameworks
   - Obtain scale type through sysfs

  New Functionality:
   - Provide Device Tree functionality in rave-sp-backlight
   - Calculate if scale type is (non-)linear in pwm_bl

  Fix-ups:
   - Simplify code in lm3630a_bl
   - Trivial rename/whitespace/typo fixes in lms283gf05
   - Remove superfluous NULL check in tosa_lcd
   - Fix power state initialisation in gpio_backlight
   - List supported file in MAINTAINERS

  Bug Fixes:
   - Kconfig - default to not building unless requested in
     {LED,BACKLIGHT}_CLASS_DEVICE"

* tag 'backlight-next-5.4' of git://git.kernel.org/pub/scm/linux/kernel/git/lee/backlight:
  backlight: pwm_bl: Set scale type for brightness curves specified in the DT
  backlight: pwm_bl: Set scale type for CIE 1931 curves
  backlight: Expose brightness curve type through sysfs
  MAINTAINERS: Add entry for stable backlight sysfs ABI documentation
  backlight: gpio-backlight: Correct initial power state handling
  video: backlight: tosa_lcd: drop check because i2c_unregister_device() is NULL safe
  video: backlight: Drop default m for {LCD,BACKLIGHT_CLASS_DEVICE}
  backlight: lms283gf05: Fix a typo in the description passed to 'devm_gpio_request_one()'
  backlight: lm3630a: Switch to use fwnode_property_count_uXX()
  backlight: rave-sp: Leave initial state and register with correct device

Documentation/ABI/testing/sysfs-class-backlight

@@ -0,0 +1,26 @@
+What:		/sys/class/backlight/<backlight>/scale
+Date:		July 2019
+KernelVersion:	5.4
+Contact:	Daniel Thompson <daniel.thompson@linaro.org>
+Description:
+		Description of the scale of the brightness curve.
+
+		The human eye senses brightness approximately logarithmically,
+		hence linear changes in brightness are perceived as being
+		non-linear. To achieve a linear perception of brightness changes
+		controls like sliders need to apply a logarithmic mapping for
+		backlights with a linear brightness curve.
+
+		Possible values of the attribute are:
+
+		unknown
+		  The scale of the brightness curve is unknown.
+
+		linear
+		  The brightness changes linearly with each step. Brightness
+		  controls should apply a logarithmic mapping for a linear
+		  perception.
+
+		non-linear
+		  The brightness changes non-linearly with each step. Brightness
+		  controls should use a linear mapping for a linear perception.