linux-kernel - Re: [PATCH] IIO: bmp280-core.c: fix error in humidity calculation

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Date:   Sun, 2 Apr 2017 10:32:52 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Andreas Klinger <ak@...klinger.de>, knaack.h@....de,
        lars@...afoo.de, pmeerw@...erw.net, linus.walleij@...aro.org,
        ddvlad@...il.com, akinobu.mita@...il.com,
        yongjun_wei@...ndmicro.com.cn, a.mathur@...sung.com
Cc:     linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] IIO: bmp280-core.c: fix error in humidity calculation

On 27/03/17 11:06, Andreas Klinger wrote:
> While calculating the compensation of the humidity there are negative
> values interpreted as unsigned because of unsigned variables used.
> These values need to be casted to signed as indicated by the documentation
> of the sensor.
> 
> Signed-off-by: Andreas Klinger <ak@...klinger.de>
Looks superficially right to me, but would like an Ack from Linus Walleij.

Linus?

J
> ---
>  drivers/iio/pressure/bmp280-core.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iio/pressure/bmp280-core.c b/drivers/iio/pressure/bmp280-core.c
> index 4d18826ac63c..73308f0ea260 100644
> --- a/drivers/iio/pressure/bmp280-core.c
> +++ b/drivers/iio/pressure/bmp280-core.c
> @@ -177,9 +177,9 @@ static u32 bmp280_compensate_humidity(struct bmp280_data *data,
>  
>  	var = ((s32)data->t_fine) - 76800;
>  	var = ((((adc_humidity << 14) - (H4 << 20) - (H5 * var)) + 16384) >> 15)
> -		* (((((((var * H6) >> 10) * (((var * H3) >> 11) + 32768)) >> 10)
> -		+ 2097152) * H2 + 8192) >> 14);
> -	var -= ((((var >> 15) * (var >> 15)) >> 7) * H1) >> 4;
> +		* (((((((var * H6) >> 10) * (((var * (s32)H3) >> 11) + 32768))
> +		>> 10) + 2097152) * H2 + 8192) >> 14);
> +	var -= ((((var >> 15) * (var >> 15)) >> 7) * (s32)H1) >> 4;
>  
>  	return var >> 12;
>  };
>