[Letux-kernel] [PATCH] pyra: Fix flickering keyboard backlight

[H. Nikolaus Schaller]

> Am 08.08.2020 um 11:56 schrieb David Shah <dave at ds0.me>:
> 
> Increase PWM frequency to 8300Hz as LM3699 datasheet recommends a
> frequency between 2kHz and 100kHz.

Yes, that is right!

The 83 Hz (12000000) is probably from (too) simply copying from the (old) display backlight which was limited to ca. 200 Hz.

What I am not sure is if all mainboard variants have the lm3699 or if we must patch specific variants.

BR and thanks,
Nikolaus

> 
> Signed-off-by: David Shah <dave at ds0.me>
> ---
> arch/arm/boot/dts/pyra-mainboard-common.dtsi | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm/boot/dts/pyra-mainboard-common.dtsi b/arch/arm/boot/dts/pyra-mainboard-common.dtsi
> index 67aca9b084de..91691c4f25de 100644
> --- a/arch/arm/boot/dts/pyra-mainboard-common.dtsi
> +++ b/arch/arm/boot/dts/pyra-mainboard-common.dtsi
> @@ -88,7 +88,7 @@ modem_en: modem {
> 
> 	keyboard-backlight {
> 		compatible = "pwm-backlight";
> -		pwms = <&pwm8 0 12000000 0>;
> +		pwms = <&pwm8 0 120000 0>; // 8300Hz
> 		pwm-names = "keyboard";
> 		brightness-levels = <0 1 2 5 10 20 40 60 100>;
> 		default-brightness-level = <5>;	/* 20% */
> -- 
> 2.27.0
> 
> _______________________________________________
> Kernel mailing list
> Kernel at pyra-handheld.com
> http://pyra-handheld.com/cgi-bin/mailman/listinfo/kernel