IIO: bmp280-core.c: fix error in humidity calculation

commit ed3730c435f1a9f9559ed7762035d22d8a95adfe upstream.

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.

Signed-off-by: Andreas Klinger <ak@it-klinger.de>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Matt Ranostay <matt.ranostay@konsulko.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/iio/pressure/bmp280-core.c b/drivers/iio/pressure/bmp280-core.c
index e5a533cbd53fa58bbee3de2a7c624e2b252c62cc..f762eb8b174ae56ec39d62ff063963e85167a728 100644 (file)
--- 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;
 };