Hello Hendrik, On Wed, Jun 10, 2020 at 03:45:07PM +0200, Hendrik Hoeth wrote: > Hi, > > I've discovered an over-/underflow problem for relative humidity > measurements in drivers/iio/pressure/bmp280-core.c. At very low > humidities the value measured by the sensor can fluctuate into the > negative humidity range. The kernel driver then reports this as > extremely large value (e.g. 4193085, corresponding to 4193% RH). The > same probably happens at high humidity values, but with our climate > chamber I was only able to look at the low end. > > To avoid this, the reference code in the BME-280 datasheet catches > values < 0% RH and > 100% RH. These two lines are currently missing in > the kernel driver. > > Attached you find a patch that fixed the problem for us. You can find > the sensor datasheet at > https://ae-bst.resource.bosch.com/media/_tech/media/datasheets/BST-BME280-DS002.pdf > The code I'm talking about is in section 4.2.3 on page 25/26. > > Thanks a lot, > > Hendrik Seems this particular issue has been already fixed here: dee2dabc0e4115b80945fe2c91603e634f4b4686 iio: bmp280: fix compensation of humidity > > -- > Garrecht Avionik GmbH | Wieslocher Str. 38 | 69190 Walldorf > https://www.air-avionics.com/ > Tel.: +49 6224 98 96 999 > Fix underflow / overflow for humidity measurements > > diff --git a/drivers/iio/pressure/bmp280-core.c b/drivers/iio/pressure/bmp280-core.c > index 29c209cc1108..d1f36b044f05 100644 > --- a/drivers/iio/pressure/bmp280-core.c > +++ b/drivers/iio/pressure/bmp280-core.c > @@ -270,6 +270,8 @@ static u32 bmp280_compensate_humidity(struct bmp280_data *data, > * (((var * (s32)calib->H3) >> 11) + (s32)32768)) >> 10) > + (s32)2097152) * calib->H2 + 8192) >> 14); > var -= ((((var >> 15) * (var >> 15)) >> 7) * (s32)calib->H1) >> 4; > + var = ((var < 0) ? 0 : var); > + var = ((var > 419430400) ? 419430400 : var); > > return var >> 12; > };
