iio: gyro: mpu3050: Fix reported temperature value

The raw temperature value is a 16-bit signed integer. The sign casting
is missing in the code, which results in a wrong temperature reported
by userspace tools, fix it.

Cc: [email protected]
Fixes: 3904b28 ("iio: gyro: Add driver for the MPU-3050 gyroscope")
Datasheet: https://www.cdiweb.com/datasheets/invensense/mpu-3000a.pdf
Tested-by: Maxim Schwalm <[email protected]> # Asus TF700T
Tested-by: Svyatoslav Ryhel <[email protected]> # Asus TF201
Reported-by: Svyatoslav Ryhel <[email protected]>
Reviewed-by: Andy Shevchenko <[email protected]>
Reviewed-by: Linus Walleij <[email protected]>
Signed-off-by: Dmitry Osipenko <[email protected]>

drivers/iio/gyro/mpu3050-core.c

@@ -272,7 +272,16 @@ static int mpu3050_read_raw(struct iio_dev *indio_dev,
 	case IIO_CHAN_INFO_OFFSET:
 		switch (chan->type) {
 		case IIO_TEMP:
-			/* The temperature scaling is (x+23000)/280 Celsius */
+			/*
+			 * The temperature scaling is (x+23000)/280 Celsius,
+			 * where 23000 includes room temperature offset of
+			 * +35C, 280 is the precision scale and x is the 16-bit
+			 * signed integer which corresponds to the "best fit
+			 * straight line" temperature range of -30C..85C.
+			 *
+			 * Temperature value itself represents temperature of
+			 * the sensor die.
+			 */
 			*val = 23000;
 			return IIO_VAL_INT;
 		default:
@@ -329,7 +338,7 @@ static int mpu3050_read_raw(struct iio_dev *indio_dev,
 				goto out_read_raw_unlock;
 			}
 
-			*val = be16_to_cpu(raw_val);
+			*val = (s16)be16_to_cpu(raw_val);
 			ret = IIO_VAL_INT;
 
 			goto out_read_raw_unlock;