Re: [PATCH v2 6/6] riscv: dts: spacemit: Add CTF2301 on K3 CoM260

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] PWM duty cycle calculation can overflow and wrap around to 0, completely turning off the fan when maximum speed is requested.
--

--- Patch [6]: [PATCH v2 6/6] riscv: dts: spacemit: Add CTF2301 on K3 CoM260 ---
commit 2adeea2e46046fc26168a60ad26929de961f2f43
Author: Troy Mitchell <troy.mitchell@linux.dev>

riscv: dts: spacemit: Add CTF2301 on K3 CoM260

This commit enables I2C6 on the K3 CoM260 module. It sets the I2C6 pin power
source and describes the Sensylink CTF2301 temperature sensor and fan
controller.

> diff --git a/arch/riscv/boot/dts/spacemit/k3-com260.dtsi b/arch/riscv/boot/dts/spacemit/k3-com260.dtsi
> index a38d7b738258d..95a60fbb411f8 100644
> --- a/arch/riscv/boot/dts/spacemit/k3-com260.dtsi
> +++ b/arch/riscv/boot/dts/spacemit/k3-com260.dtsi
> @@ -26,6 +26,25 @@ reg_5v_sys: regulator-5v-sys {
>  	};
>  };
>  
> +&pinctrl {
> +	i2c6-1-cfg {
> +		i2c6-1-pins {
> +			power-source = <3300>;
> +		};
> +	};
> +};
> +
> +&i2c6 {
> +	pinctrl-names = "default";
> +	pinctrl-0 = <&i2c6_1_cfg>;
> +	status = "okay";
> +
> +	temperature-sensor@4c {
> +		compatible = "sensylink,ctf2301";

[Severity: High]
This isn't a bug introduced by this patch, but adding this sensor node
exposes a pre-existing PWM duty cycle calculation overflow in the lm63
driver.

When the fan controller computes the duty cycle in drivers/hwmon/lm63.c:

drivers/hwmon/lm63.c:lm63_pwm_to_reg() {
    ...
    return (val * data->pwm1_freq * 2 + LM63_MAX_PWM / 2) / LM63_MAX_PWM;
}

If the bootloader configures a low PWM frequency (setting the register > 127),
data->pwm1_freq will exceed 127 without bounds checking.

When maximum cooling is requested (val = 255), the arithmetic evaluates to
256 or more. Because the function returns a u8, the value implicitly
truncates and wraps around to 0.

Can this completely turn off the fan when maximum cooling is requested?

> +		reg = <0x4c>;
> +	};
> +};

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260721-ctl2301-v2-0-ef5fb342872a@linux.dev?part=6