linux-kernel - Re: [PATCH v2] IIO: bmp280-core.c: fix error in humidity calculation

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Date:   Fri, 14 Apr 2017 15:13:16 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Matt Ranostay <matt.ranostay@...sulko.com>,
        Andreas Klinger <ak@...klinger.de>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald <pmeerw@...erw.net>,
        Vlad Dogaru <ddvlad@...il.com>,
        Akinobu Mita <akinobu.mita@...il.com>,
        Wei Yongjun <yongjun_wei@...ndmicro.com.cn>,
        Aniroop Mathur <a.mathur@...sung.com>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] IIO: bmp280-core.c: fix error in humidity calculation

On 12/04/17 00:59, Matt Ranostay wrote:
> On Mon, Apr 10, 2017 at 10:00 AM, Andreas Klinger <ak@...klinger.de> wrote:
>> While calculating the compensation of the humidity there are negative values
>> interpreted as unsigned because of unsigned variables used.  These values as
>> well as the constants need to be casted to signed as indicated by the
>> documentation of the sensor.
>>
>> Changes in v2:
>> - cast also constants to signed; otherwise calculation is not correct
>>
>> I removed the Acked-By of Linus Walleij because of another change in the
>> calculation. Don't know how it should be treated.
>>
>> Signed-off-by: Andreas Klinger <ak@...klinger.de>
> 
> Reviewed-by: Matt Ranostay <matt.ranostay@...sulko.com>
Applied to the fixes-togreg branch of iio.git and marked for
stable.

Thanks,

Jonathan
> 
>> ---
>>  drivers/iio/pressure/bmp280-core.c | 11 ++++++-----
>>  1 file changed, 6 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/iio/pressure/bmp280-core.c b/drivers/iio/pressure/bmp280-core.c
>> index 4d18826ac63c..d82b788374b6 100644
>> --- a/drivers/iio/pressure/bmp280-core.c
>> +++ b/drivers/iio/pressure/bmp280-core.c
>> @@ -175,11 +175,12 @@ static u32 bmp280_compensate_humidity(struct bmp280_data *data,
>>         }
>>         H6 = sign_extend32(tmp, 7);
>>
>> -       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 = ((s32)data->t_fine) - (s32)76800;
>> +       var = ((((adc_humidity << 14) - (H4 << 20) - (H5 * var))
>> +               + (s32)16384) >> 15) * (((((((var * H6) >> 10)
>> +               * (((var * (s32)H3) >> 11) + (s32)32768)) >> 10)
>> +               + (s32)2097152) * H2 + 8192) >> 14);
>> +       var -= ((((var >> 15) * (var >> 15)) >> 7) * (s32)H1) >> 4;
>>
>>         return var >> 12;
>>  };
>> --
>> 2.1.4
>>
>>
>> --