`On Wed, 21 Oct 2020, Alexandru Stan wrote:> The previous behavior was a little unexpected, its properties/problems:> 1. It was designed to generate strictly increasing values (no repeats)> 2. It had quantization errors when calculating step size. Resulting in> unexpected jumps near the end of some segments.> > Example settings:> 	brightness-levels = <0 1 2 4 8 16 32 64 128 256>;> 	num-interpolated-steps = <16>;> > Whenever num-interpolated-steps was larger than the distance> between 2 consecutive brightness levels the table would get really> discontinuous. The slope of the interpolation would stick with> integers only and if it was 0 the whole line segment would get skipped.> > The distances between 1 2 4 and 8 would be 1 (property #1 fighting us),> and only starting with 16 it would start to interpolate properly.> > Property #1 is not enough. The goal here is more than just monotonically> increasing. We should still care about the shape of the curve. Repeated> points might be desired if we're in the part of the curve where we want> to go slow (aka slope near 0).> > Problem #2 is plainly a bug. Imagine if the 64 entry was 63 instead,> the calculated slope on the 32-63 segment will be almost half as it> should be.> > The most expected and simplest algorithm for interpolation is linear> interpolation, which would handle both problems.> Let's just implement that!> > Take pairs of points from the brightness-levels array and linearly> interpolate between them. On the X axis (what userspace sees) we'll> now have equally sized intervals (num-interpolated-steps sized,> as opposed to before where we were at the mercy of quantization).> > ENDI removed this.> Signed-off-by: Alexandru Stan <amstan@chromium.org>> ---> >  drivers/video/backlight/pwm_bl.c | 70 ++++++++++++++------------------>  1 file changed, 31 insertions(+), 39 deletions(-)Applied, thanks.-- Lee Jones [李琼斯]Senior Technical Lead - Developer ServicesLinaro.org │ Open source software for Arm SoCsFollow Linaro: Facebook | Twitter | Blog`