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 is currently opaque
to userspace, so userspace often relies on 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 a new sysfs attribute.
Matthias Kaehlcke (4):
MAINTAINERS: Add entry for stable backlight sysfs ABI documentation
backlight: Expose brightness curve type through sysfs
backlight: pwm_bl: Set scale type for CIE 1931 curves
backlight: pwm_bl: Set scale type for brightness curves specified in
the DT
.../ABI/testing/sysfs-class-backlight | 32 +++++++++++++++++++
MAINTAINERS | 2 ++
drivers/video/backlight/backlight.c | 22 +++++++++++++
drivers/video/backlight/pwm_bl.c | 30 ++++++++++++++++-
include/linux/backlight.h | 10 ++++++
5 files changed, 95 insertions(+), 1 deletion(-)
create mode 100644 Documentation/ABI/testing/sysfs-class-backlight
--
2.22.0.rc2.383.gf4fbbf30c2-goog
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