iio: mxs-lradc: Fix temperature offset

commit b94e22805a2224061bb263a82b72e09544a5fbb3 upstream.

0° Kelvin is actually −273.15°C, not -272.15°C. Fix the temperature offset.
Also improve the comment explaining the calculation.

Reported-by: Janusz Użycki <j.uzycki@elpromaelectronics.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Stefan Wahren <stefan.wahren@i2se.com>
Acked-by: Marek Vasut <marex@denx.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/iio/adc/mxs-lradc.c b/drivers/staging/iio/adc/mxs-lradc.c
index 27e1a6e62d069894345c6f0d085084b3ec34b31b..503846c3e6207d961b4f103d0a29673adff4b0aa 100644 (file)
--- a/drivers/staging/iio/adc/mxs-lradc.c
+++ b/drivers/staging/iio/adc/mxs-lradc.c
@@ -920,11 +920,12 @@ static int mxs_lradc_read_raw(struct iio_dev *iio_dev,
        case IIO_CHAN_INFO_OFFSET:
                if (chan->type == IIO_TEMP) {
                        /* The calculated value from the ADC is in Kelvin, we
-                        * want Celsius for hwmon so the offset is
-                        * -272.15 * scale
+                        * want Celsius for hwmon so the offset is -273.15
+                        * The offset is applied before scaling so it is
+                        * actually -213.15 * 4 / 1.012 = -1079.644268
                         */
-                       *val = -1075;
-                       *val2 = 691699;
+                       *val = -1079;
+                       *val2 = 644268;
 
                        return IIO_VAL_INT_PLUS_MICRO;
                }