On Tue, 09 Jul 2019, Matthias Kaehlcke wrote:
Backlight brightness curves can have different shapes. The two main types are linear and non-linear curves. The human eye doesn't perceive linearly increasing/decreasing brightness as linear (see also 88ba95bedb79 "backlight: pwm_bl: Compute brightness of LED linearly to human eye"), hence many backlights use non-linear (often logarithmic) brightness curves. The type of curve currently is opaque to userspace, so userspace often uses more or less reliable heuristics (like the number of brightness levels) to decide whether to treat a backlight device as linear or non-linear.
Export the type of the brightness curve via the new sysfs attribute 'scale'. The value of the attribute can be 'linear', 'non-linear' or 'unknown'. For devices that don't provide information about the scale of their brightness curve the value of the 'scale' attribute is 'unknown'.
Signed-off-by: Matthias Kaehlcke mka@chromium.org
Feel free to suggest improvements in the documentation :)
Changes in v3:
- removed composite strings, only keep 'linear', 'non-linear' and 'unknown'
- updated sysfs attribute documentation
- updated commit message
Changes in v2:
- changed order of brightness scale enums, explicitly make 'unknown' zero
- minor update of commit message
- deleted excess blank line after 'backlight_scale_types'
- s/curves/curve/ in sysfs doc
.../ABI/testing/sysfs-class-backlight | 26 +++++++++++++++++++ MAINTAINERS | 1 + drivers/video/backlight/backlight.c | 19 ++++++++++++++ include/linux/backlight.h | 8 ++++++ 4 files changed, 54 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-class-backlight
Applied, thanks.