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

[Pei Xiao]

在 2026/6/9 23:41, Cryolitia PukNgae 写道:
>
> On 6/9/26 07:41, 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@xxxxxxxxxx>
>> ---
>>   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 */
>>       return DIV_ROUND_CLOSEST((var - 1) * 255, (drvdata->pwm_max - 1));
>>   }
>>   
>
> Have you ever tested the behavior on a real device? When it returns 0,
> what state is the device in? 
>
Hi Cryolitia,

Thanks for your  messages!
Yes, this is not an issue, but this problem was reported during the Sashiko
AI review.
 The maintainer suggested I take a look. After checking, I think it might
be better to add a check: 
if it's 0, just return directly. In case some EC returns 0 someday, causing
an underflow, 
returning an error code would be more intuitive than returning an incorrect
value.

https://sashiko.dev/#/patchset/cover.1780880972.git.xiaopei01@xxxxxxxxxx?part=1

Pei.
>
> thanks,
>
> Cryolitia PukNgae