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

From: Jonathan Cameron <jic23@kernel.org>
To: Matt Ranostay <matt.ranostay@konsulko.com>,
	Andreas Klinger <ak@it-klinger.de>
Cc: Linus Walleij <linus.walleij@linaro.org>,
	Hartmut Knaack <knaack.h@gmx.de>,
	Lars-Peter Clausen <lars@metafoo.de>,
	Peter Meerwald <pmeerw@pmeerw.net>,
	Vlad Dogaru <ddvlad@gmail.com>,
	Akinobu Mita <akinobu.mita@gmail.com>,
	Wei Yongjun <yongjun_wei@trendmicro.com.cn>,
	Aniroop Mathur <a.mathur@samsung.com>,
	"linux-iio@vger.kernel.org" <linux-iio@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] IIO: bmp280-core.c: fix error in humidity calculation
Date: Fri, 14 Apr 2017 15:13:16 +0100	[thread overview]
Message-ID: <0955126a-e408-cf59-3f38-cd6daf4998ff@kernel.org> (raw)
In-Reply-To: <CAJCx=gmVtxgnWbRKRYMOjVXAVRJciZ2w-5GxUQ4D+1GwMZ4k2Q@mail.gmail.com>

On 12/04/17 00:59, Matt Ranostay wrote:
> On Mon, Apr 10, 2017 at 10:00 AM, Andreas Klinger <ak@it-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@it-klinger.de>
> 
> Reviewed-by: Matt Ranostay <matt.ranostay@konsulko.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
>>
>>
>> --