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Message-ID: <fkiauvfki7kvmhs3g4aqatqcdtf6cko7xpgg7zfhgojnhoxa36@ruz5ywsdgr4c>
Date: Mon, 5 Aug 2024 13:07:11 +0200
From: Nikola Radojevic <nikola@...ojevic.rs>
To: Dragan Simic <dsimic@...jaro.org>
Cc: linux-rockchip@...ts.infradead.org, heiko@...ech.de,
linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org, robh@...nel.org, krzk+dt@...nel.org,
conor+dt@...nel.org, linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] arm64: dts: rockchip: Raise Pinebook Pro's panel
backlight PWM frequency
Hello,
I have tested this on my Pinebook Pro and I can confirm that
everything seems to work alright.
Tested-by: Nikola Radojević <nikola@...ojevic.rs>
On 24/08/04 11:10PM, Dragan Simic wrote:
> Increase the frequency of the PWM signal that drives the LED backlight of
> the Pinebook Pro's panel, from about 1.35 KHz (which equals to the PWM
> period of 740,740 ns), to exactly 8 kHz (which equals to the PWM period of
> 125,000 ns). Using a higher PWM frequency for the panel backlight, which
> reduces the flicker, can only be beneficial to the end users' eyes.
>
> On top of that, increasing the backlight PWM signal frequency reportedly
> eliminates the buzzing emitted from the Pinebook Pro's built-in speakers
> when certain backlight levels are set, which cause some weird interference
> with some of the components of the Pinebook Pro's audio chain.
>
> The old value for the backlight PWM period, i.e. 740,740 ns, is pretty much
> an arbitrary value that was selected during the very early bring-up of the
> Pinebook Pro, only because that value seemed to minimize horizontal line
> distortion on the display, which resulted from the old X.org drivers causing
> screen tearing when dragging windows around. That's no longer an issue, so
> there are no reasons to stick with the old PWM period value.
>
> The lower and the upper backlight PWM frequency limits for the Pinebook Pro's
> panel, according to its datasheet, are 200 Hz and 10 kHz, respectively. [1]
> These changes still leave some headroom, which may have some positive effects
> on the lifetime expectancy of the panel's backlight LEDs.
>
> [1] https://files.pine64.org/doc/datasheet/PinebookPro/NV140FHM-N49_Rev.P0_20160804_201710235838.pdf
>
> Fixes: 5a65505a6988 ("arm64: dts: rockchip: Add initial support for Pinebook Pro")
> Cc: stable@...r.kernel.org
> Reported-by: Nikola Radojevic <nikola@...ojevic.rs>
> Signed-off-by: Dragan Simic <dsimic@...jaro.org>
> ---
> arch/arm64/boot/dts/rockchip/rk3399-pinebook-pro.dts | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/boot/dts/rockchip/rk3399-pinebook-pro.dts b/arch/arm64/boot/dts/rockchip/rk3399-pinebook-pro.dts
> index 294eb2de263d..b3f76cc2d6e1 100644
> --- a/arch/arm64/boot/dts/rockchip/rk3399-pinebook-pro.dts
> +++ b/arch/arm64/boot/dts/rockchip/rk3399-pinebook-pro.dts
> @@ -32,7 +32,7 @@ chosen {
> backlight: edp-backlight {
> compatible = "pwm-backlight";
> power-supply = <&vcc_12v>;
> - pwms = <&pwm0 0 740740 0>;
> + pwms = <&pwm0 0 125000 0>;
> };
>
> bat: battery {
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