2017-04-10 17:00:47

by Andreas Klinger

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

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 <[email protected]>
---
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


--

2017-04-11 07:46:35

by Linus Walleij

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

On Mon, Apr 10, 2017 at 7:00 PM, Andreas Klinger <[email protected]> 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.

Acked-by: Linus Walleij <[email protected]>

You guys do an awesome job at maintaining the sensor code, thanks.

Yours,
Linus Walleij

2017-04-11 23:59:35

by Matt Ranostay

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

On Mon, Apr 10, 2017 at 10:00 AM, Andreas Klinger <[email protected]> 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 <[email protected]>

Reviewed-by: Matt Ranostay <[email protected]>

> ---
> 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
>
>
> --

2017-04-14 14:13:22

by Jonathan Cameron

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 <[email protected]> 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 <[email protected]>
>
> Reviewed-by: Matt Ranostay <[email protected]>
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
>>
>>
>> --