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linux-next/Documentation/ABI/testing/sysfs-class-backlight
Mauro Carvalho Chehab bd6e8441c2 docs: ABI: sysfs-class-backlight: unify ABI documentation
Both adp8860 and adp8870 define some extensions to the
backlight class. This causes warnings:

	Warning: /sys/class/backlight/<backlight>/ambient_light_level is defined 2 times:  /sys/class/backlight/<backlight>/ambient_light_level:8  /sys/class/backlight/<backlight>/ambient_light_level:30
	Warning: /sys/class/backlight/<backlight>/ambient_light_zone is defined 2 times:  /sys/class/backlight/<backlight>/ambient_light_zone:18  /sys/class/backlight/<backlight>/ambient_light_zone:40

As ABI definitions shouldn't be duplicated.

Unfortunately, the ABI is dependent on the specific device
features. As such, ambient_light_level range is somewhat
different among the supported devices.

The ambient_light_zone is even worse: the meanings of each
preset are different, and there's no ABI to retrieve
the supported types nor their meanins. Unfortunately,
it is too late to fix it without causing regressions,
as this has been used since Kernel v2.6.35.

Rewrite those ABI documentation using the current documentation
as a reference, and double-checking at the datasheets:

	https://www.analog.com/media/en/technical-documentation/data-sheets/ADP8870.pdf
	https://www.analog.com/media/en/technical-documentation/data-sheets/ADP8860.pdf

in order to properly document the differences between those two
drivers.

Acked-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/342195ad5a819d9bcfcebc133c77ab69b4211672.1604042072.git.mchehab+huawei@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-10-30 13:15:01 +01:00

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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.
What: /sys/class/backlight/<backlight>/ambient_light_level
Date: Apr, 2010
KernelVersion: v2.6.35
Contact: Michael Hennerich <michael.hennerich@analog.com>
Description:
(RO) Get conversion value of the light sensor.
The value is automatically updated every 80 ms when the
light sensor is enabled.
The value range is device-driver specific:
For ADP8870:
It returns integer between 0 (dark) and 8000 (max ambient
brightness).
For ADP8860:
It returns a 13-bits integer.
What: /sys/class/backlight/<backlight>/ambient_light_zone
Date: Apr, 2010
KernelVersion: v2.6.35
Contact: Michael Hennerich <michael.hennerich@analog.com>,
device-drivers-devel@blackfin.uclinux.org
Description:
(RW) Read or write the specific brightness level at which the
backlight operates.
The value meaning is device-driver specific:
For ADP8860:
== ==========================
0 Off: Backlight set to 0 mA
1 Level 1: daylight
2 Level 2: bright
3 Level 3: dark
== ==========================
For ADP8870:
== ==========================
0 Off: Backlight set to 0 mA
1 Level 1: daylight
2 Level 2: bright
3 Level 3: office
4 Level 4: indoor
5 Level 5: dark
== ==========================
Writing 0 returns to normal/automatic ambient light level
operation.
It can be enabled by writing the value stored in
/sys/class/backlight/<backlight>/max_brightness to
/sys/class/backlight/<backlight>/brightness.