linux-kernel - Re: [PATCH] thermal/drivers/exynos_tmu: Fix warnings in temp_to_code / code_to

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Message-id: <11044079.DdDvlFD91s@amdc3058>
Date:   Fri, 13 Apr 2018 13:08:35 +0200
From:   Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     edubezval@...il.com, rui.zhang@...el.com, philip.li@...el.com,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Kukjin Kim <kgene@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        "open list:SAMSUNG THERMAL DRIVER" 
        <linux-samsung-soc@...r.kernel.org>,
        "moderated list:ARM/SAMSUNG EXYNOS ARM ARCHITECTURES" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] thermal/drivers/exynos_tmu: Fix warnings in
 temp_to_code / code_to_temp

On Friday, April 13, 2018 01:00:09 PM Daniel Lezcano wrote:
> The latest driver cleanup introduced a compilation warning
> 
>  drivers/thermal/samsung/exynos_tmu.c: In function ‘exynos_get_temp’:
>  drivers/thermal/samsung/exynos_tmu.c:931:37: warning: ‘temp’ may be used uninitialized in this function [-Wmaybe-uninitialized]
>    *temp = code_to_temp(data, value) * MCELSIUS;
>                                         ^
> 
>  drivers/thermal/samsung/exynos_tmu.c: In function ‘temp_to_code’
>  drivers/thermal/samsung/exynos_tmu.c:304:9: warning: ‘temp_code’ may be used uninitialized in this function [-Wmaybe-uninitialized]
> 					  return temp_code;
> 					           ^~~~~~~~~
> 
> The compiler gives a warning because semantically speaking the
> function has no default value. However the code path, were the
> variable is never initialized is a dead branch because the switch
> statement always choose one of the two cases as the data->cal_type is
> initialized in the init function to one of both values.
> 
> This is unclear as it adds a dependency on the initialization function
> and it is prone to error. Make things clearer by converting the
> functions with if ... return statements, thus showing we are expecting
> the values to be correctly filled before calling this function.
> 
> This change fixes the couple of function warnings.
> 
> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>

Thanks Daniel, this is much better fix.

Acked-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>

> ---
>  drivers/thermal/samsung/exynos_tmu.c | 46 ++++++++++--------------------------
>  1 file changed, 12 insertions(+), 34 deletions(-)
> 
> diff --git a/drivers/thermal/samsung/exynos_tmu.c b/drivers/thermal/samsung/exynos_tmu.c
> index 2ec8548..197f267 100644
> --- a/drivers/thermal/samsung/exynos_tmu.c
> +++ b/drivers/thermal/samsung/exynos_tmu.c
> @@ -284,24 +284,13 @@ static void exynos_report_trigger(struct exynos_tmu_data *p)
>   */
>  static int temp_to_code(struct exynos_tmu_data *data, u8 temp)
>  {
> -	int temp_code;
> -
> -	switch (data->cal_type) {
> -	case TYPE_TWO_POINT_TRIMMING:
> -		temp_code = (temp - EXYNOS_FIRST_POINT_TRIM) *
> -			(data->temp_error2 - data->temp_error1) /
> -			(EXYNOS_SECOND_POINT_TRIM - EXYNOS_FIRST_POINT_TRIM) +
> -			data->temp_error1;
> -		break;
> -	case TYPE_ONE_POINT_TRIMMING:
> -		temp_code = temp + data->temp_error1 - EXYNOS_FIRST_POINT_TRIM;
> -		break;
> -	default:
> -		WARN_ON(1);
> -		break;
> -	}
> +	if (data->cal_type == TYPE_ONE_POINT_TRIMMING)
> +		return temp + data->temp_error1 - EXYNOS_FIRST_POINT_TRIM;
>  
> -	return temp_code;
> +	return (temp - EXYNOS_FIRST_POINT_TRIM) *
> +		(data->temp_error2 - data->temp_error1) /
> +		(EXYNOS_SECOND_POINT_TRIM - EXYNOS_FIRST_POINT_TRIM) +
> +		data->temp_error1;
>  }
>  
>  /*
> @@ -310,24 +299,13 @@ static int temp_to_code(struct exynos_tmu_data *data, u8 temp)
>   */
>  static int code_to_temp(struct exynos_tmu_data *data, u16 temp_code)
>  {
> -	int temp;
> -
> -	switch (data->cal_type) {
> -	case TYPE_TWO_POINT_TRIMMING:
> -		temp = (temp_code - data->temp_error1) *
> -			(EXYNOS_SECOND_POINT_TRIM - EXYNOS_FIRST_POINT_TRIM) /
> -			(data->temp_error2 - data->temp_error1) +
> -			EXYNOS_FIRST_POINT_TRIM;
> -		break;
> -	case TYPE_ONE_POINT_TRIMMING:
> -		temp = temp_code - data->temp_error1 + EXYNOS_FIRST_POINT_TRIM;
> -		break;
> -	default:
> -		WARN_ON(1);
> -		break;
> -	}
> +	if (data->cal_type == TYPE_ONE_POINT_TRIMMING)
> +		return temp_code - data->temp_error1 + EXYNOS_FIRST_POINT_TRIM;
>  
> -	return temp;
> +	return (temp_code - data->temp_error1) *
> +		(EXYNOS_SECOND_POINT_TRIM - EXYNOS_FIRST_POINT_TRIM) /
> +		(data->temp_error2 - data->temp_error1) +
> +		EXYNOS_FIRST_POINT_TRIM;
>  }
>  
>  static void sanitize_temp_error(struct exynos_tmu_data *data, u32 trim_info)

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics