[PATCH 4.9 066/164] IIO: bmp280-core.c: fix error in humidity calculation

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andreas Klinger <ak@xxxxxxxxxxxxx>

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@xxxxxxxxxxxxx>
Acked-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
Reviewed-by: Matt Ranostay <matt.ranostay@xxxxxxxxxxxx>
Signed-off-by: Jonathan Cameron <jic23@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/iio/pressure/bmp280-core.c |   11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

--- a/drivers/iio/pressure/bmp280-core.c
+++ b/drivers/iio/pressure/bmp280-core.c
@@ -175,11 +175,12 @@ static u32 bmp280_compensate_humidity(st
 	}
 	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;
 };