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  • Matthias Kaehlcke's avatar
    backlight: Expose brightness curve type through sysfs · d55c028f
    Matthias Kaehlcke authored
    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 88ba95be
    
     "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: default avatarMatthias Kaehlcke <mka@chromium.org>
    Reviewed-by: default avatarDaniel Thompson <daniel.thompson@linaro.org>
    Signed-off-by: default avatarLee Jones <lee.jones@linaro.org>
    d55c028f