[PATCH 0/3] backlight: lm3630a: add functionality to change boost converter frequency

[Maximilian Weigand]

For certain brightness settings the Pine64 PineNote exhibits quite
visible flickering of the led backlights, leading to an unpleasant user
experience. It is understood that flickering is caused by certain power
line ripples interacting with the led driver, inherent to the
specific hardware. The lm3630a led driver is able to change the boost
converter switching frequency. Among other things, changing the boost
frequency can also greatly improve visible flickering issues.

This patchset enables dts control of two frequency modifications that the
hardware is capable of: Switch from a base frequency of 500 kHz to 1
MHz, and activate a frequency shift to 560 kHz or 1.12 MHz,
respectively.

As flickering characteristics are mainly hardware dependent, this should
warrant the inclusion of two dts entries for the lm3630a led driver to
control the boost frequency of the chip on a per-device basis.

Changes were tested on a Pine64 PineNote. The following brightness
settings were found to exhibit serious flickering without either the
frequency shift or the higher boost frequency:

echo 186 > /sys/class/backlight/backlight_warm/brightness
echo 255 > /sys/class/backlight/backlight_cool/brightness

Signed-off-by: Maximilian Weigand <mweigand at mweigand.net>
---
Maximilian Weigand (3):
      backlight: lm3630a: add support for changing the boost frequency
      dt-bindings: backlight: lm3630a: add entries to control boost frequency
      arm64: dts: rockchip: shift boost frequency for rk3566-pinenote backlight

 .../bindings/leds/backlight/lm3630a-backlight.yaml           | 12 ++++++++++++
 arch/arm64/boot/dts/rockchip/rk3566-pinenote.dtsi            |  1 +
 drivers/video/backlight/lm3630a_bl.c                         |  9 ++++++++-
 include/linux/platform_data/lm3630a_bl.h                     |  5 +++++
 4 files changed, 26 insertions(+), 1 deletion(-)
---
base-commit: 858fd168a95c5b9669aac8db6c14a9aeab446375
change-id: 20230602-lm3630a_boost_frequency-bae9656ec759

Best regards,
-- 
Maximilian Weigand <mweigand at mweigand.net>