I was trying to adjust the brightness for a new chromebook: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/2... Like a lot of panels, the low end needs to be cropped, and now that we have the interpolation stuff I wanted to make use of it and bake in even the curve.
I found the behavior a little unintuitive and non-linear. See patch 1 for a suggested fix for this.
Unfortunatelly a few veyron dts files were relying on this (perhaps weird) behavior. Those devices also want a minimum brightness. The issue is that they also want the 0% point for turning off the display. https://github.com/torvalds/linux/commit/6233269bce47bd450196a671ab28eb1ec5e...
So the idea here is to change those dts files to only say <3 255> (patch 3), and add in a virtual 0% point at the bottom of the scale (patch 2).
We have to do this conditionally because it seems some devices like to have the scale inverted: % git grep "brightness-levels\s*=\s*<\s*[1-9]"|cat arch/arm/boot/dts/tegra124-apalis-eval.dts: brightness-levels = <255 231 223 207 191 159 127 0>;
Alexandru Stan (3): backlight: pwm_bl: Fix interpolation backlight: pwm_bl: Artificially add 0% during interpolation ARM: dts: rockchip: Remove 0 point in backlight
arch/arm/boot/dts/rk3288-veyron-jaq.dts | 2 +- arch/arm/boot/dts/rk3288-veyron-minnie.dts | 2 +- arch/arm/boot/dts/rk3288-veyron-tiger.dts | 2 +- drivers/video/backlight/pwm_bl.c | 78 +++++++++++----------- 4 files changed, 42 insertions(+), 42 deletions(-)