linux-kernel - [PATCH v1] iio: gyro: mpu3050: Fix reported temperature value

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Date:   Thu, 22 Apr 2021 02:48:20 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Linus Walleij <linus.walleij@...aro.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Maxim Schwalm <maxim.schwalm@...il.com>,
        Svyatoslav Ryhel <clamor95@...il.com>
Cc:     linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v1] iio: gyro: mpu3050: Fix reported temperature value

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

Cc: stable@...r.kernel.org
Link: https://www.cdiweb.com/datasheets/invensense/mpu-3000a.pdf
Tested-by: Maxim Schwalm <maxim.schwalm@...il.com> # Asus TF700T
Tested-by: Svyatoslav Ryhel <clamor95@...il.com> # Asus TF201
Reported-by: Svyatoslav Ryhel <clamor95@...il.com>
Signed-off-by: Dmitry Osipenko <digetx@...il.com>
---
 drivers/iio/gyro/mpu3050-core.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/gyro/mpu3050-core.c b/drivers/iio/gyro/mpu3050-core.c
index ac90be03332a..9885428ca12e 100644
--- 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,
+			 * where 23000 includes room temperature offset of
+			 * +35C, 280 is the precision scale and x is the signed
+			 * 16bit integer which corresponds to the temperature
+			 * range of -40C..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;
-- 
2.30.2