[Bug 1340544] Re: gnome-rr: Normalize the minimum brightness level.

[Shih-Yuan Lee]

** Summary changed:

- gnome-rr: Adjust the minimum brightness level when the maximum >= 100.
+ gnome-rr: Normalize the minimum brightness level.

** Description changed:

- If the maximum brightness is equal to or bigger than 100, it has higher
- possibility that zero is off. So adjusting the minimum brightness to avoid the problem.
+ This patch is aimed to normalize the minimum brightness level for 20
+ brightness steps used in gnome-settings-daemon and bring a better and
+ consistent user experience for the brigtness control in
+ gnome-settings-daemon and gnome-control-center.
+ 
+ For example, most Intel Haswell/Broadwell UMA laptops have the same 937
+ value as their maximum brightness level on Linux kernel 3.16 by default.
+ 
+ By this patch, the minimum brightness level will be changed to 17
+ because 937 / 20 == 46 and 937 % 46 == 17, and 17 is a reasonable and
+ visible brightness level as the minimum brightness level on these laptops.
+ If we set 0 to /sys/class/backlight/intel_backlight/brightness, it makes
+ the screen off.
+ If we set 1 to /sys/class/backlight/intel_backlight/brightness, the
+ screen becomes hard to see the content.
+ So 17 is a better brightness level.
+ 
+ This patch should not affect existing ACPI brightness control especially
+ for those laptops having the maximum brightness level under 20.
+ 
+ This also avoided the screen off when using the minimum brightness level
+ under some condition.
  
  Quotes from
  http://cgit.freedesktop.org/xorg/proto/randrproto/tree/randrproto.txt
  
  "This property controls the brightness on laptop panels and equivalent
   displays with a backlight controller. The driver specific maximum
   value MUST turn the backlight to full brightness, 1 SHOULD turn the
   backlight to minimum brightness, 0 SHOULD turn the backlight off."
  
  Quotes from http://msdn.microsoft.com/en-
  us/library/windows/hardware/ff569755(v=vs.85).aspx
  
  "Brightness levels are represented as single-byte values in the range
   from zero to 100 where zero is off and 100 is the maximum brightness
   that a laptop computer supports. Every laptop computer must report a
   maximum brightness level of 100; however, a laptop computer is not
   required to support a level of zero. The only requirement for values
   from zero to 100 is that larger values must represent higher brightness
   levels."

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https://bugs.launchpad.net/bugs/1340544

Title:
  gnome-rr: Normalize the minimum brightness level.

Status in GNOME Desktop Common Files:
  New
Status in Gnome Settings Daemon:
  New
Status in Unity Settings Daemon:
  New
Status in “gnome-desktop3” package in Ubuntu:
  New

Bug description:
  This patch is aimed to normalize the minimum brightness level for 20
  brightness steps used in gnome-settings-daemon and bring a better and
  consistent user experience for the brigtness control in
  gnome-settings-daemon and gnome-control-center.

  For example, most Intel Haswell/Broadwell UMA laptops have the same 937
  value as their maximum brightness level on Linux kernel 3.16 by default.

  By this patch, the minimum brightness level will be changed to 17
  because 937 / 20 == 46 and 937 % 46 == 17, and 17 is a reasonable and
  visible brightness level as the minimum brightness level on these laptops.
  If we set 0 to /sys/class/backlight/intel_backlight/brightness, it makes
  the screen off.
  If we set 1 to /sys/class/backlight/intel_backlight/brightness, the
  screen becomes hard to see the content.
  So 17 is a better brightness level.

  This patch should not affect existing ACPI brightness control especially
  for those laptops having the maximum brightness level under 20.

  This also avoided the screen off when using the minimum brightness
  level under some condition.

  Quotes from
  http://cgit.freedesktop.org/xorg/proto/randrproto/tree/randrproto.txt

  "This property controls the brightness on laptop panels and equivalent
   displays with a backlight controller. The driver specific maximum
   value MUST turn the backlight to full brightness, 1 SHOULD turn the
   backlight to minimum brightness, 0 SHOULD turn the backlight off."

  Quotes from http://msdn.microsoft.com/en-
  us/library/windows/hardware/ff569755(v=vs.85).aspx

  "Brightness levels are represented as single-byte values in the range
   from zero to 100 where zero is off and 100 is the maximum brightness
   that a laptop computer supports. Every laptop computer must report a
   maximum brightness level of 100; however, a laptop computer is not
   required to support a level of zero. The only requirement for values
   from zero to 100 is that larger values must represent higher brightness
   levels."

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