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.

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>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

diff --git a/drivers/iio/pressure/bmp280-core.c b/drivers/iio/pressure/bmp280-core.c
index 4d18826ac63c2eca6bde3c03e18600961a885c11..d82b788374b61ba617bc5a073e17d283e5e0cfc9 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;
 };