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[Linux] PWM problems

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Posted at 5/12/2023 22:32:00     
  • Type: Self-Compiled Firmware
  • SDK Package Name: rk356x_linux_release_v1.3.0b_20221213
  • Last Commit: 0000-00-00 00:00:00
  • Modification Content: LVDS with PWM configuration
  • Log: no log.zip
Problem description and steps to reproduce:
I have a custom board based on RK3568jq.
I made Linux minimal image using Yocto:
https://wiki.t-firefly.com/en/Fi ... e/manual_yocto.html
I added PWM control and it works fine using next command:echo 100 > /sys/class/backlight/backlight/brightness


but as i can see using oscilloscope , the frequency of PWM signal is about 40 seconds instead of 20 kHz !



my dtsi-file modifications:
rk3568-firefly-roc-pc.dtsi


backlight:backlight {
        status = "okay";        
        compatible = "pwm-backlight";
        pwms = <&pwm4 0 50000 0>;
...
}

lvds_panel: lvds-panel {
        compatible = "simple-panel";
        status = "okay";
        backlight = <&backlight>;
.....
}


what im doing wrong about frequency?
The third paramenter 50000 is frequency in nanoseconds ?

pwms = <&pwm4 0 50000 0>;






no log.zip

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Posted at 5/15/2023 17:45:54     
The 50000 is means 50000ns.
If you need to set the maximum clock frequency, please use 'echo 255 > /sys/class/backlight/backlight/brightness'.
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