Re: [PATCH] hwmon: (gpd-fan) Reject EC PWM value 0 as invalid

[Guenter Roeck <linux@roeck-us.net>]

On Tue, Jun 09, 2026 at 03:41:35PM +0800, Pei Xiao wrote:
> The EC firmware is expected to return values in [1, pwm_max]. A read of 0
> is illegal and would cause underflow in the conversion formula. Explicitly
> check for 0 and return -EIO.
> 
> Signed-off-by: Pei Xiao <xiaopei01@kylinos.cn>
> ---
>  drivers/hwmon/gpd-fan.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hwmon/gpd-fan.c b/drivers/hwmon/gpd-fan.c
> index d1993cd645cb..decb61936b95 100644
> --- a/drivers/hwmon/gpd-fan.c
> +++ b/drivers/hwmon/gpd-fan.c
> @@ -341,7 +341,11 @@ static int gpd_wm2_read_pwm(struct gpd_fan_data *data)
>  
>  	gpd_ecram_read(drvdata, drvdata->pwm_write, &var);
>  
> -	// Match gpd_generic_write_pwm(u8) below
> +	/* EC PWM register valid range is 1 ~ pwm_max; 0 is an invalid state */
> +	if (unlikely(!var))
> +		return -EIO;
> +
> +	/* Match gpd_generic_write_pwm() below */

Please do not change to comment format in an existing driver.
This driver uses the C++ comment style.

Thanks,
Guenter

>  	return DIV_ROUND_CLOSEST((var - 1) * 255, (drvdata->pwm_max - 1));
>  }
>