fan continously runs on kernel 5.8 but I need to use 5. kernel for PCIe sata card

[GreyLinux]

You can apply the overlay a few different ways - you can use the fdtoverlay tool from the device-tree-compiler package to take the base .dtb and the compiled overlay and write the result to a compiled flat device tree:

Code:

fdtoverlay -i base.dtb -o base_with_overlay.dtb overlay.dtbo

... then use the base_with_overlay.dtb to boot.

Or you can get U-boot to load and apply it in-memory during boot - it sounds like Armbian supports this for Allwinner but maybe not for Rockchip? I have not been using Armbian so I don't know the details of how this works. I use a custom U-Boot script to apply the overlays using the fdt apply command.

Whether or not this is better than running the fan constantly depends on what you want - I have an open case with the fan mounted on the CPU heatsink, so it makes sense to control it according to the CPU temperature reading. It is normally off unless I'm compiling something using all 6 cores. For your use-case, it sounds like you have the NAS case and so maybe have the fan mounted on the case, not the CPU heatsink, and the fan is cooling not only the board but some HDDs, so maybe it is better to run the fan all the time to cool the whole case - depends what you think really.

Hearing you explain it I think your right, with a sealed case, the tall heatsink, the 80mm case fan and trying to cool the SSD's as well I should probably have it running all the time just at a lower speed rather than flat out. I think ill just add

Code:

echo 128 > /sys/devices/platform/pwm-fan/hwmon/hwmon0/pwm1

 to the /etc/rc.local file and have it control the fan speed manually at boot.

I'll run some some tests to see what is the best value to use the fan at for my setup .

I appreciate you taking the time to explain how to apply overlays to the device tree I will definitely be doing more research into this, now that I understand it a little better,
its a very interesting topic that I've seen mentioned a few times but never really understood it or gave it much thought .

thanks again for your help and advice .