backlight: pwm_bl: Compute brightness of LED linearly to human eye
When you want to change the brightness using a PWM signal, one thing you need to consider is how human perceive the brightness. Human perceive the brightness change non-linearly, we have better sensitivity at low luminance than high luminance, so to achieve perceived linear dimming, the brightness must be matches to the way our eyes behave. The CIE 1931 lightness formula is what actually describes how we perceive light. This patch computes a default table with the brightness levels filled with the numbers provided by the CIE 1931 algorithm, the number of the brightness levels is calculated based on the PWM resolution. The calculation of the table using the CIE 1931 algorithm is enabled by default when you do not define the 'brightness-levels' propriety in your device tree. Signed-off-by: NEnric Balletbo i Serra <enric.balletbo@collabora.com> Acked-by: NDaniel Thompson <daniel.thompson@linaro.org> Signed-off-by: NLee Jones <lee.jones@linaro.org>
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