PWM fan control not working with Rock5B and upstream kernel

[Qu Wenruo]

Hi,

My Rock5B board is running edk-rk3588 firmware and (almost) upstream 
kernel (6.14.6 kernel from ArchlinuxARM), using upstream dtbs (the 
firmware is also switched to device-tree boot mode)

Before that I'm using ACPI mode thus no PMW support, but the firmware's 
fan control is working properly although running at a fixed rpm setting.

But after switching to the upstream kernel and device-tree mode, the pwm 
fan control never works.

`sensors` command detects the fan, and the pwm seems to properly 
following the temperature, but the physical fan just do not spin at all:

center_thermal-virtual-0
Adapter: Virtual device
temp1:        +80.4°C

bigcore2_thermal-virtual-0
Adapter: Virtual device
temp1:        +84.1°C

package_thermal-virtual-0
Adapter: Virtual device
temp1:        +81.3°C

pwmfan-isa-0000
Adapter: ISA adapter
pwm1:            128%  MANUAL CONTROL <<<

gpu_thermal-virtual-0
Adapter: Virtual device
temp1:        +79.5°C

littlecore_thermal-virtual-0
Adapter: Virtual device
temp1:        +82.2°C

bigcore0_thermal-virtual-0
Adapter: Virtual device
temp1:        +83.2°C


I'm wondering is this a bug in the upstream PWM code or something else 
is missing preventing the fan from working properly.

Thanks,
Qu