linux-kernel - Re: [PATCH v1 3/3] thermal: tsens: Fix negative temperature reporting

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Message-ID: <20180725234936.GT129942@google.com>
Date:   Wed, 25 Jul 2018 16:49:36 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Amit Kucheria <amit.kucheria@...aro.org>
Cc:     linux-kernel@...r.kernel.org, rnayak@...eaurora.org,
        linux-arm-msm@...r.kernel.org, bjorn.andersson@...aro.org,
        edubezval@...il.com, smohanad@...eaurora.org,
        andy.gross@...aro.org, dianders@...omium.org,
        Zhang Rui <rui.zhang@...el.com>, linux-pm@...r.kernel.org
Subject: Re: [PATCH v1 3/3] thermal: tsens: Fix negative temperature reporting

On Wed, Jul 18, 2018 at 12:55:03PM +0530, Amit Kucheria wrote:
> The current code will always return 0xffffffff in case of negative
> temperatures due to a bug in how the binary sign extension is being done.
> 
> Use sign_extend32() instead.
> 
> Signed-off-by: Amit Kucheria <amit.kucheria@...aro.org>
> ---
>  drivers/thermal/qcom/tsens-v2.c | 13 +++++--------
>  1 file changed, 5 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/thermal/qcom/tsens-v2.c b/drivers/thermal/qcom/tsens-v2.c
> index 908e3dc..46abc21 100644
> --- a/drivers/thermal/qcom/tsens-v2.c
> +++ b/drivers/thermal/qcom/tsens-v2.c
> @@ -5,19 +5,20 @@
>   */
>  
>  #include <linux/regmap.h>
> +#include <linux/bitops.h>
>  #include "tsens.h"
>  
>  #define STATUS_OFFSET		0xa0
>  #define LAST_TEMP_MASK		0xfff
>  #define STATUS_VALID_BIT	BIT(21)
> -#define CODE_SIGN_BIT		BIT(11)
>  
>  static int get_temp_tsens_v2(struct tsens_device *tmdev, int id, int *temp)
>  {
>  	struct tsens_sensor *s = &tmdev->sensor[id];
>  	u32 code;
>  	unsigned int status_reg;
> -	int last_temp = 0, last_temp2 = 0, last_temp3 = 0, ret;
> +	u32 last_temp = 0, last_temp2 = 0, last_temp3 = 0;
> +	int ret;
>  
>  	status_reg = tmdev->tm_offset + STATUS_OFFSET + s->hw_id * 4;
>  	ret = regmap_read(tmdev->map, status_reg, &code);
> @@ -54,12 +55,8 @@ static int get_temp_tsens_v2(struct tsens_device *tmdev, int id, int *temp)
>  	else if (last_temp2 == last_temp3)
>  		last_temp = last_temp3;
>  done:
> -	/* Code sign bit is the sign extension for a negative value */
> -	if (last_temp & CODE_SIGN_BIT)
> -		last_temp |= ~CODE_SIGN_BIT;
> -
> -	/* Temperatures are in deciCelicius */
> -	*temp = last_temp * 100;
> +	/* Convert temperatures to milliCelicius */

nits:

s/temperatures/temperature/
s/milliCelicius/milliCelsius/

> +	*temp = sign_extend32(last_temp, fls(LAST_TEMP_MASK) - 1) * 100;
>  
>  	return 0;
>  }

Reviewed-by: Matthias Kaehlcke <mka@...omium.org>