linux-kernel - Re: [PATCH] iio: scd4x: check return of scd4x_write_and

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Date:   Mon, 28 Feb 2022 13:06:32 -0800
From:   Tom Rix <trix@...hat.com>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     roan@...tonic.nl, lars@...afoo.de, nathan@...nel.org,
        ndesaulniers@...gle.com, linux-iio@...r.kernel.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] iio: scd4x: check return of scd4x_write_and_fetch


On 2/27/22 9:48 AM, Jonathan Cameron wrote:
> On Sun, 27 Feb 2022 07:43:31 -0800
> trix@...hat.com wrote:
>
>> From: Tom Rix <trix@...hat.com>
>>
>> Clang static analysis reports this problem
>> scd4x.c:474:10: warning: The left operand of '==' is a
>>    garbage value
>>    if (val == 0xff) {
>>        ~~~ ^
>> val is only set from a successful call to scd4x_write_and_fetch()
>> So check it's return.
>>
>> Fixes: 49d22b695cbb ("drivers: iio: chemical: Add support for Sensirion SCD4x CO2 sensor")
>> Signed-off-by: Tom Rix <trix@...hat.com>
> Good find, but I'd prefer a separate check on ret inline with what the
> other error checking paths in that function are doing.
>
>> ---
>>   drivers/iio/chemical/scd4x.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/iio/chemical/scd4x.c b/drivers/iio/chemical/scd4x.c
>> index 20d4e7584e923..b978330fb761c 100644
>> --- a/drivers/iio/chemical/scd4x.c
>> +++ b/drivers/iio/chemical/scd4x.c
>> @@ -471,7 +471,7 @@ static ssize_t calibration_forced_value_store(struct device *dev,
>>   	ret = scd4x_write_and_fetch(state, CMD_FRC, arg, &val, sizeof(val));
>>   	mutex_unlock(&state->lock);
>>   
>> -	if (val == 0xff) {
>> +	if (!ret && val == 0xff) {
>>   		dev_err(dev, "forced calibration has failed");
>>   		return -EINVAL;
>>   	}
> Prefer
>
> 	if (ret)
> 		return ret;
>
> 	if (val == 0xff) {
> 		dev_err(dev, "...
> 		return -EINVAL;
> 	}

ok and the next line can be simplified to

return len;

Tom

> Thanks,
>
> Jonathan
>