Re: [PATCH v5 6/6] arm64: dts: rockchip: Add cooling fan to ROCK 4D

[Nicolas Frattaroli <nicolas.frattaroli@collabora.com>]

Hello,

On Sunday, 26 April 2026 09:23:01 Central European Summer Time Damon Ding wrote:
> Hi Nicolas,
> 
> On 4/20/2026 9:52 PM, Nicolas Frattaroli wrote:
> > The ROCK 4D has a header to connect a small cooling fan. This fan is
> > driven by one of the SoC's PWM outputs driving a transistor, that in
> > turn controls the fan's power.
> > 
> > With the introduction of PWM support, add a description of this cooling
> > fan, as well as the additional trips and cooling-maps for it.
> > 
> > Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
> > ---
> >   arch/arm64/boot/dts/rockchip/rk3576-rock-4d.dts | 50 +++++++++++++++++++++++++
> >   1 file changed, 50 insertions(+)
> > 
> > diff --git a/arch/arm64/boot/dts/rockchip/rk3576-rock-4d.dts b/arch/arm64/boot/dts/rockchip/rk3576-rock-4d.dts
> > index 899a84b1fbf9..2d5ede010ad0 100644
> > --- a/arch/arm64/boot/dts/rockchip/rk3576-rock-4d.dts
> > +++ b/arch/arm64/boot/dts/rockchip/rk3576-rock-4d.dts
> > @@ -45,6 +45,14 @@ rfkill {
> >   		shutdown-gpios = <&gpio2 RK_PD1 GPIO_ACTIVE_HIGH>;
> >   	};
> >   
> > +	fan: pwm-fan {
> > +		compatible = "pwm-fan";
> > +		cooling-levels = <0 180 205 230 255>;
> > +		fan-supply = <&vcc_5v0_sys>;
> > +		pwms = <&pwm2_8ch_5 0 60000 0>;
> > +		#cooling-cells = <2>;
> > +	};
> > +
> >   	leds: leds {
> >   		compatible = "gpio-leds";
> >   		pinctrl-names = "default";
> > @@ -711,6 +719,36 @@ rgmii_phy0: ethernet-phy@1 {
> >   	};
> >   };
> >   
> > +&package_thermal {
> > +	polling-delay = <100>;
> > +
> > +	trips {
> > +		package_fan0: package-fan0 {
> > +			temperature = <50000>;
> > +			hysteresis = <2000>;
> > +			type = "active";
> > +		};
> > +
> > +		package_fan1: package-fan1 {
> > +			temperature = <60000>;
> > +			hysteresis = <2000>;
> > +			type = "active";
> > +		};
> > +	};
> > +
> > +	cooling-maps {
> > +		map1 {
> > +			trip = <&package_fan0>;
> > +			cooling-device = <&fan THERMAL_NO_LIMIT 1>;
> > +		};
> > +
> > +		map2 {
> > +			trip = <&package_fan1>;
> > +			cooling-device = <&fan 2 THERMAL_NO_LIMIT>;
> > +		};
> > +	};
> > +};
> > +
> >   &pcie0 {
> >   	pinctrl-names = "default";
> >   	pinctrl-0 = <&pcie_reset>;
> > @@ -720,6 +758,13 @@ &pcie0 {
> >   };
> >   
> >   &pinctrl {
> > +	fan {
> > +		fan_pwm: fan-pwm {
> > +			rockchip,pins =
> > +				<4 RK_PC5 14 &pcfg_pull_down_drv_level_5>;
> > +		};
> > +	};
> > +
> >   	hym8563 {
> >   		hym8563_int: hym8563-int {
> >   			rockchip,pins = <0 RK_PA0 RK_FUNC_GPIO &pcfg_pull_up>;
> > @@ -770,6 +815,11 @@ wifi_en_h: wifi-en-h {
> >   	};
> >   };
> >   
> > +&pwm2_8ch_5 {
> > +	pinctrl-0 = <&fan_pwm>;
> 
> May I ask why the pinctrl does not directly use &pwm2m1_ch5?
> 
> Is it because the default pin configuration cannot meet the requirements 
> of the fan?

Yes, I'm adding a strong pull down. The PWM pin controls a transistor,
and if it floats when not in use the fan can start spinning when no
PWM signal is present. If I recall correctly (it's been a while since
I wrote this DT patch) it could be left spinning when the board was
shut down with a `poweroff` command.

> 
> > +	status = "okay";
> > +};
> > +
> >   &sai6 {
> >   	status = "okay";
> >   };
> > 
> 
> Best regards,
> Damon
> 
> 

Kind regards,
Nicolas Frattaroli