How to OrangePi5+ (OrangePi5plus) pwm fan fix

This manual are for Armbian (other distro can be adapted).

Decompile current dtb to text.

$ mkdir ~/my-dt
$ cp /boot/dtb/rockchip/rk3588-orangepi-5-plus.dtb ~/my-dt/original.dtb
$ dtc -I dtb -O dts -o ~/my-dt/dts.txt ~/my-dt/original.dtb

Open dts.txt and find "pwm-fan" section. Look at "pwms" record.

For example: < A B C D >

"B and D both are zero".

"A" is link to pwm3.

"C" is MOST IMPORTANT - it's PERIOD of ns (frequency).

Here is example (Your pwm-fan section can look slight different) :

pwm-fan {
    compatible = "pwm-fan";
    #cooling-cells = <0x02>;
    pwms = <0x1f2 0x00 0xc350 0x00>;
    cooling-levels = <0x00 0x32 0x64 0x96 0xc8 0xff>;
    rockchip,temp-trips = <0xc350 0x01 0xd6d8 0x02 0xea60 0x03 0xfde8 0x04 0x11170 0x05>;
    status = "okay";
    phandle = <0x4ac>;
};

We can see "50000" or "0xc350", at 3rd parameter. It's 50'000 ns period (0xc350) = 20`000Hz = 20kHz.

Pwm-fan schematic has RC-chain (R23+C16): 10K+100nF.

Fc=1/(2piRC)=1/0.00628=160Hz.

So, current DeviceTree settings with 20kHz acts as DC-voltage control (ON/OFF) with max fan speed under any conditions.

You can desolder C16 capacitor, to solve this problem!

(Can you really can locate this cap_0402 on unsilcscreeneed pcb?).

The other way is to reduce pwm frequency to 100Hz!

To reduce frequency replace 3rd pwms parameter to "10000000" (one+7zeros) = "10 million" (nanoseconds) = 0.01s = 100Hz.

Here is example:

pwm-fan {
    compatible = "pwm-fan";
    #cooling-cells = <0x02>;
    pwms = <0x1f2 0x00 10000000 0x00>;
    cooling-levels = <0x00 0x32 0x64 0x96 0xc8 0xff>;
    rockchip,temp-trips = <0xc350 0x01 0xd6d8 0x02 0xea60 0x03 0xfde8 0x04 0x11170 0x05>;
    status = "okay";
    phandle = <0x4ac>;
};

Take look at pwms record 3rd parameter replaced with 10000000. Your pwm-fan section can look slight different, but only one replacement you need to do, is change 3rd pwms parameter to 10000000.

Compile current text to dtb and replace boot-dtb.

$ dtc -I dts -O dtb -o ~/my-dt/new.dtb ~/my-dt/dts.txt
$ sudo cp -f ~/my-dt/new.dtb /boot/dtb/rockchip/rk3588-orangepi-5-plus.dtb
$ sudo reboot

Your OrangePi5+ fan works at different speeds now!

PS: You can directly change pwm-speed of fan using "/sys"-file.

Here is Debian11(Armbian) example.

$ su
# echo 127 > /sys/devices/platform/pwm-fan/hwmon/hwmon9/pwm1

Pls, replace "127"(half of 255) with more values like "255"(full-speed), "127"(half-speed), "64 (one-quater-speed)", "192 = 3/4 speed" and etc.

NOTE: But sometimes in nearest future, the driver will drop this value to "0" due current tempereture measurement.

PS2: 50Hz, 90Hz, 100Hz, 120Hz, 125Hz, 150Hz ... ?

Due to very low frequency, human ear can listen(!) low frequency from fan. This effect has known as "rumble sound from fan" at pwm-low speed pulses. You can do experiency with something other basic frequencies as 50,100,125,150, but below then 160Hz.

Some of fans are really silent at 100-150Hz of low pwm. Please, try it.