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: stable@vger.kernel.org
Fixes: 3904b28efb2c ("iio: gyro: Add driver for the MPU-3050 gyroscope")
Datasheet: https://www.cdiweb.com/datasheets/invensense/mpu-3000a.pdf
Tested-by: Maxim Schwalm <maxim.schwalm@gmail.com> # Asus TF700T
Tested-by: Svyatoslav Ryhel <clamor95@gmail.com> # Asus TF201
Reported-by: Svyatoslav Ryhel <clamor95@gmail.com>
Reviewed-by: Andy Shevchenko <Andy.Shevchenko@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Jean-Baptiste Maneyrol <jmaneyrol@invensense.com>
Link: https://lore.kernel.org/r/20210423020959.5023-1-digetx@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/drivers/iio/gyro/mpu3050-core.c b/drivers/iio/gyro/mpu3050-core.c
index ac90be0..f17a935 100644 (file)
--- a/drivers/iio/gyro/mpu3050-core.c
+++ b/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
+                        * for the "best fit straight line" temperature range
+                        * of -30C..85C.  The 23000 includes room temperature
+                        * offset of +35C, 280 is the precision scale and x is
+                        * the 16-bit signed integer reported by hardware.
+                        *
+                        * 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;