linux-kernel - Re: [PATCH v2 01/11] hwmon: (amc6821) Stop accepting invalid pwm values

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Message-ID: <846630f6-64a2-412d-8436-c71c21618461@roeck-us.net>
Date: Wed, 3 Jul 2024 13:17:47 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Quentin Schulz <quentin.schulz@...rry.de>, linux-hwmon@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, Farouk Bouabid <farouk.bouabid@...rry.de>
Subject: Re: [PATCH v2 01/11] hwmon: (amc6821) Stop accepting invalid pwm
 values

On 7/3/24 07:29, Quentin Schulz wrote:
> Hi Guenter,
> 
> On 7/1/24 11:23 PM, Guenter Roeck wrote:
>> The pwm value range is well defined from 0..255. Don't accept
>> any values outside this range.
>>
>> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
>> ---
>> v2: Use kstrtou8() instead of kstrtol() where possible.
>>      Limit range of pwm1_auto_point_pwm to 0..254 in patch 1
>>      instead of limiting it later, and do not accept invalid
>>      values for the attribute.
>>
>>   drivers/hwmon/amc6821.c | 15 +++++++++------
>>   1 file changed, 9 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/hwmon/amc6821.c b/drivers/hwmon/amc6821.c
>> index 9b02b304c2f5..eb2d5592a41a 100644
>> --- a/drivers/hwmon/amc6821.c
>> +++ b/drivers/hwmon/amc6821.c
>> @@ -355,13 +355,13 @@ static ssize_t pwm1_store(struct device *dev,
>>   {
>>       struct amc6821_data *data = dev_get_drvdata(dev);
>>       struct i2c_client *client = data->client;
>> -    long val;
>> -    int ret = kstrtol(buf, 10, &val);
>> +    u8 val;
>> +    int ret = kstrtou8(buf, 10, &val);
>>       if (ret)
>>           return ret;
>>       mutex_lock(&data->update_lock);
>> -    data->pwm1 = clamp_val(val , 0, 255);
>> +    data->pwm1 = val;
>>       i2c_smbus_write_byte_data(client, AMC6821_REG_DCY, data->pwm1);
>>       mutex_unlock(&data->update_lock);
>>       return count;
>> @@ -558,13 +558,16 @@ static ssize_t pwm1_auto_point_pwm_store(struct device *dev,
>>       struct amc6821_data *data = dev_get_drvdata(dev);
>>       struct i2c_client *client = data->client;
>>       int dpwm;
>> -    long val;
>> -    int ret = kstrtol(buf, 10, &val);
>> +    u8 val;
>> +    int ret = kstrtou8(buf, 10, &val);
>>       if (ret)
>>           return ret;
>>
>> +    if (val > 254)
> 
> Would have appreciated a comment as to why it's 254. My understanding is that the subsystem requires no overlap between multiple pwm_auto_points? 0 being 0 and 2 being 255, we need 1 to be 255?
> 

No idea, really, I just took it from the original code. I don't find a hint
in the code suggesting why 255 would be worse than 0.

> Actually, that doesn't explain why we allow 0 here, so maybe I'm just clueless :)
> 
Yes, agreed, that doesn't really make sense. I'll change the upper limit to 255.

> The change itself though:
> Reviewed-by: Quentin Schulz <quentin.schulz@...rry.de>
> 
... but I'll also keep that tag unless you start screaming.

Thanks,
Guenter