Hi Uwe,
On Fri, Aug 16, 2019 at 06:51:48PM +0200, Uwe Kleine-König wrote:
On Tue, Jul 09, 2019 at 12:00:05PM -0700, 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
I wonder what kind of problem you are solving here. Can you describe that in a few words?
The human eye perceives brightness in a logarithmic manner. For backlights with a linear brightness curve brightness controls like sliders need to use a mapping to achieve a behavior that is perceived as linear-ish (more details: http://www.pathwaylighting.com/products/downloads/brochure/technical_materia...)
As of now userspace doesn't have information about the type of the brightness curve, and often uses heuristics to make a guess, which may be right most of the time, but not always. The new attribute eliminates the need to guess.