linux-kernel - [PATCH 4.14 290/323] iio: gyro: mpu3050: Fix reported temperature value

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Message-Id: <20210520092130.151303166@linuxfoundation.org>
Date:   Thu, 20 May 2021 11:23:02 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Svyatoslav Ryhel <clamor95@...il.com>,
        Andy Shevchenko <Andy.Shevchenko@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Dmitry Osipenko <digetx@...il.com>,
        Jean-Baptiste Maneyrol <jmaneyrol@...ensense.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Maxim Schwalm <maxim.schwalm@...il.com>
Subject: [PATCH 4.14 290/323] iio: gyro: mpu3050: Fix reported temperature value

From: Dmitry Osipenko <digetx@...il.com>

commit f73c730774d88a14d7b60feee6d0e13570f99499 upstream.

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@...r.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@...il.com> # Asus TF700T
Tested-by: Svyatoslav Ryhel <clamor95@...il.com> # Asus TF201
Reported-by: Svyatoslav Ryhel <clamor95@...il.com>
Reviewed-by: Andy Shevchenko <Andy.Shevchenko@...il.com>
Reviewed-by: Linus Walleij <linus.walleij@...aro.org>
Signed-off-by: Dmitry Osipenko <digetx@...il.com>
Acked-by: Jean-Baptiste Maneyrol <jmaneyrol@...ensense.com>
Link: https://lore.kernel.org/r/20210423020959.5023-1-digetx@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/iio/gyro/mpu3050-core.c |   13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

--- a/drivers/iio/gyro/mpu3050-core.c
+++ b/drivers/iio/gyro/mpu3050-core.c
@@ -270,7 +270,16 @@ static int mpu3050_read_raw(struct iio_d
 	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:
@@ -327,7 +336,7 @@ static int mpu3050_read_raw(struct iio_d
 				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;