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

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Date:   Sun, 27 Feb 2022 17:48:50 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     trix@...hat.com
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 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;
	}

Thanks,

Jonathan