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arm64: dts: rockchip: Raise Pinebook Pro's panel backlight PWM frequency

Message ID 2a23b6cfd8c0513e5b233b4006ee3d3ed09b824f.1722805655.git.dsimic@manjaro.org (mailing list archive)
State New
Headers show
Series arm64: dts: rockchip: Raise Pinebook Pro's panel backlight PWM frequency | expand

Commit Message

Dragan Simic Aug. 4, 2024, 9:10 p.m. UTC
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@vger.kernel.org
Reported-by: Nikola Radojevic <nikola@radojevic.rs>
Signed-off-by: Dragan Simic <dsimic@manjaro.org>
---
 arch/arm64/boot/dts/rockchip/rk3399-pinebook-pro.dts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Nikola Radojevic Aug. 5, 2024, 11:07 a.m. UTC | #1
Hello,
I have tested this on my Pinebook Pro and I can confirm that
everything seems to work alright.

Tested-by: Nikola Radojević <nikola@radojevic.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@vger.kernel.org
> Reported-by: Nikola Radojevic <nikola@radojevic.rs>
> Signed-off-by: Dragan Simic <dsimic@manjaro.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 {
Heiko Stuebner Aug. 10, 2024, 9:59 p.m. UTC | #2
On Sun, 4 Aug 2024 23:10:24 +0200, 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.
> 
> [...]

Applied, thanks!

[1/1] arm64: dts: rockchip: Raise Pinebook Pro's panel backlight PWM frequency
      commit: 8c51521de18755d4112a77a598a348b38d0af370

Best regards,
diff mbox series

Patch

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 {