linux-kernel - Re: [PATCH 3/3] riscv: dts: thead: th1520: add soft PWM fan for Lichee Pi 4A

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Message-ID: <aKjh6hrhrRqUvnSd@x1>
Date: Fri, 22 Aug 2025 14:32:26 -0700
From: Drew Fustini <fustini@...nel.org>
To: Icenowy Zheng <uwu@...nowy.me>
Cc: Guo Ren <guoren@...nel.org>, Fu Wei <wefu@...hat.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Han Gao <rabenda.cn@...il.com>,
	Yao Zi <ziyao@...root.org>, linux-riscv@...ts.infradead.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] riscv: dts: thead: th1520: add soft PWM fan for
 Lichee Pi 4A

On Sat, Aug 16, 2025 at 05:32:09PM +0800, Icenowy Zheng wrote:
> Because of the SoM+Dock design of Lichee Pi 4A, heat dissipation does
> not work well; fortunately it comes with a fan port with PWM driving
> capability.
> 
> As the hardware PWM controller of Lichee Pi 4A isn't ready yet, drive it
> with pwm-gpio driver (software PWM) now.
> 
> A long PWM period is used, because not only software PWM is used, but
> also the fan port is a 2-pin one and fast PWM might confuse the BLDC
> driver on fans.
> 
> Signed-off-by: Icenowy Zheng <uwu@...nowy.me>
> ---
>  .../boot/dts/thead/th1520-lichee-pi-4a.dts    | 53 +++++++++++++++++++
>  arch/riscv/boot/dts/thead/th1520.dtsi         |  2 +-
>  2 files changed, 54 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/boot/dts/thead/th1520-lichee-pi-4a.dts b/arch/riscv/boot/dts/thead/th1520-lichee-pi-4a.dts
> index 4020c727f09e8..f696db01353c5 100644
> --- a/arch/riscv/boot/dts/thead/th1520-lichee-pi-4a.dts
> +++ b/arch/riscv/boot/dts/thead/th1520-lichee-pi-4a.dts
> @@ -4,6 +4,7 @@
>   */
>  
>  #include "th1520-lichee-module-4a.dtsi"
> +#include <dt-bindings/gpio/gpio.h>
>  
>  / {
>  	model = "Sipeed Lichee Pi 4A";
> @@ -28,6 +29,58 @@ aliases {
>  	chosen {
>  		stdout-path = "serial0:115200n8";
>  	};
> +
> +	gpio_pwm: gpio-pwm {
> +		#pwm-cells = <3>;
> +		compatible = "pwm-gpio";
> +		gpios = <&gpio3 3 GPIO_ACTIVE_HIGH>;
> +	};

I think the node name needs to be 'pwm' instead of 'gpio-pwm' as dtbs_check
warns that:

gpio-pwm: $nodename:0: 'gpio-pwm' does not match '^pwm(@.*|-([0-9]|[1-9][0-9]+))?$'
from schema $id: http://devicetree.org/schemas/pwm/pwm-gpio.yaml#

Thanks,
Drew