[PATCH] arm64: dts: rockchip: pwm-fan overlay for NanoPC-T6

[Hugh Cole-Baker]

On 27/10/2025 09:14, Alexey Charkov wrote:
> Hi Hugh,
> 
> On Mon, Oct 27, 2025 at 1:09 PM Hugh Cole-Baker <sigmaris at gmail.com> wrote:
>>
>> FriendlyELEC offers an optional heatsink and fan addon for the NanoPC-T6
>> and T6 LTS. Add an overlay which can be applied if the fan is fitted and
>> configures the fan as an active cooling device for the SoC package.
>>
>> Signed-off-by: Hugh Cole-Baker <sigmaris at gmail.com>
>> ---
>> FriendlyELEC heatsink with fan addon:
>> https://www.friendlyelec.com/index.php?route=product/product&product_id=305
>> Vendor DT with trip points and PWM duty cycle values:
>> https://github.com/friendlyarm/kernel-rockchip/blob/4944602540b62f5aad139fe602a76cf7c3176128/arch/arm64/boot/dts/rockchip/rk3588-nanopi6-rev01.dts#L75-L90

Hi Alexey,

> Is there any downside to enabling this unconditionally in the board
> .dts?

Only that it goes against the principle that the DT should describe the
hardware; the board .dts would describe a cooling device that doesn't
actually exist on the base board.

I guess then in theory, an OS might allow the SoC to reach undesirably high
temperatures if it's relying on the nonexistent fan to cool it down. But I
don't think this would be an issue on Linux, at least, in practice.

> Overlays require more user configuration, and not all
> bootloaders support them directly (e.g. systemd-boot users would
> struggle). Compiling with overlays enabled also makes .dtb's a lot
> larger due to added symbols information.

Nowadays (on Debian at least) using overlays is pretty easy, I'm using the
u-boot-menu package in Debian, I just copy the overlay(s) to /boot/dtbo/ and
it detects them automatically and adds them to extlinux.conf for u-boot to
apply.

Couldn't systemd-boot users just use rk3588-nanopc-t6-(lts-)with-fan.dtb as
their single DT to load, if it doesn't support applying overlays and they
want to use the fan addon?

FWIW, I haven't noticed any problems with having a larger .dtb (using mainline
U-Boot to load it) and several other RK3588 boards are also compiled with
symbols enabled already, and I haven't seen any issues reported with them.

Best regards,
Hugh