CVS commit: src/sys/arch/arm/dts

["matthew green" <mrg%netbsd.org@localhost>]

Module Name:    src
Committed By:   mrg
Date:           Tue Aug 13 04:24:07 UTC 2024

Modified Files:
        src/sys/arch/arm/dts: rk3399-pinebook-pro.dts

Log Message:
apply a DTS change from upstream to reduce pwm frequency for the backlight.

should fix buzzing sometimes seen with the display.  do this as an override
rather than patching the dts source.  (tested with a hack to ensure that
the new value is set in the configuration.)

XXX: pullup-10, perhaps pullup-9.

upstream commit message:

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

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@localhost
Reported-by: Nikola Radojevic <nikola%radojevic.rs@localhost>
Signed-off-by: Dragan Simic <dsimic%manjaro.org@localhost>
Tested-by: Nikola Radojevi# <nikola%radojevic.rs@localhost>
Link: https://lore.kernel.org/r/2a23b6cfd8c0513e5b233b4006ee3d3ed09b824f.1722805655.git.dsimic%manjaro.org@localhost
Signed-off-by: Heiko Stuebner <heiko%sntech.de@localhost>


To generate a diff of this commit:
cvs rdiff -u -r1.7 -r1.8 src/sys/arch/arm/dts/rk3399-pinebook-pro.dts

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.