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 -- 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; };
