I have an HDMI display that doesn't support backlight control via the HDMI port, so I'm trying to do it using some spare GPIO pin, using a device tree overlay. Here's my overlay:
The overlay compiles and loads fine.
`sudo cat /sys/kernel/debug/pwm` shows:`pinctrl get 18-19,27` shows:/boot/config.txt is stock with only the following modifications:`pwm-backlight` is the overlay displayed above.
`ls /sys/class/backlight/backlight``actual_brightness` is 255, and `brightness` is also 255. I see no errors in the logs, so everything appears to be loading as expected. However, I get no PWM signal on GPIO 18; it remains low. I also tried setting `brightness` to 128, but while it succeeded without error, the signal on GPIO 18 remains low.
What am I doing wrong?
`uname -a` is:
Code:
/dts-v1/;/plugin/;/ { compatible = "brcm,bcm2835"; fragment@0 { target = <&gpio>; __overlay__ { pwm_pins: pwm_pins { brcm,pins = <18 19>; brcm,function = <2>; brcm,pull = <0>; }; }; }; fragment@1 { target = <&pwm>; __overlay__ { pinctrl-names = "default"; pinctrl-0 = <&pwm_pins>; status = "okay"; }; }; fragment@2 { target-path = "/"; __overlay__ { backlight: backlight { compatible = "pwm-backlight"; pwms = <&pwm 0 200000>; brightness-levels = <0 255>; num-interpolated-steps = <255>; default-brightness-level = <255>; enable-gpios = <&gpio 27 1>; }; }; };};`sudo cat /sys/kernel/debug/pwm` shows:
Code:
platform/fe20c000.pwm, 2 PWM devices pwm-0 (backlight ): requested period: 200000 ns duty: 0 ns polarity: normal pwm-1 ((null) ): period: 0 ns duty: 0 ns polarity: normalCode:
18: a5 pn | lo // GPIO18 = PWM0_019: a5 pn | lo // GPIO19 = PWM0_127: op -- pd | hi // GPIO27 = outputCode:
dtparam=audio=offdtoverlay=pwm-backlight`ls /sys/class/backlight/backlight`
Code:
actual_brightness bl_power brightness device max_brightness power scale subsystem type ueventWhat am I doing wrong?
`uname -a` is:
Code:
Linux raspberrypi 6.1.0-rpi7-rpi-v8 #1 SMP PREEMPT Debian 1:6.1.63-1+rpt1 (2023-11-24) aarch64 GNU/LinuxStatistics: Posted by JinShil — Tue Jan 16, 2024 11:59 pm — Replies 1 — Views 303