[PATCH v2] iio: gyro: mpu3050: Fix reported temperature value

[PATCH v2] iio: gyro: mpu3050: Fix reported temperature value

[Dmitry Osipenko]

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>
---

Changelog:

v2: - Replaced "signed 16bit integer" wording with "16-bit signed integer",
      replaced "Link" tag with the "Datasheet" and added "Fixes" tag as was
      suggested by Andy Shevchenko.

    - Added r-b from Andy Shevchenko and Linus Walleij.

 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..ce9d1d3687f5 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 16-bit
+			 * signed 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

Re: [PATCH v1] iio: gyro: mpu3050: Fix reported temperature value

[Dmitry Osipenko]

22.04.2021 09:46, Andy Shevchenko пишет:
>                     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
>     temperature
>     +                        * range of -40C..85C.
> 
> 
> 
> Datasheet says typical -30°... also think about the other comment you
> gave, I.e. about temperature of the die itself. Are you suggesting that
> at -40° the die T is also -40°?  Does it have perpetuum mobile ? ;) it
> might dissipate not to much energy, but we don’t know the linearity of
> the curve there.

My understanding that -40C is the minimum temperature which sensor may
report.

Alright, I think the comment could be improved a tad anyways. I'll
prepare v3, thanks.