gnome-rr: Normalize the minimum brightness level.

[Shih-Yuan Lee]

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."

[Martin Pitt (pitti)]

Let's wait for the resolution on the upstream bug before sponsoring this.

[Shih-Yuan Lee (fourdollars)]

I revised my patches to make the brightness minimum level more consistent than previous implementation.
Now it needs to patch gnome-desktop3, gnome-settings-daemon and unity-settings-daemon.
I will update my patches to the upstream bug afterward.

[Iain Lane (laney)]

Thanks for working upstream. Let's wait until the solution described there has taken place.

[Shih-Yuan Lee (fourdollars)]

I found this issue is fixed in Linux kernel.
Please see http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=6dda730e55f412a6dfb181cae6784822ba463847.