linux-kernel - [PATCH 3.16.y-ckt 48/94] iio: mxs-lradc: Fix temperature offset

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Date:	Fri, 13 Nov 2015 10:09:42 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	Jonathan Cameron <jic23@...nel.org>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 48/94] iio: mxs-lradc: Fix temperature offset

3.16.7-ckt20 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Alexandre Belloni <alexandre.belloni@...e-electrons.com>

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@...romaelectronics.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Acked-by: Stefan Wahren <stefan.wahren@...e.com>
Acked-by: Marek Vasut <marex@...x.de>
Signed-off-by: Jonathan Cameron <jic23@...nel.org>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 drivers/staging/iio/adc/mxs-lradc.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/staging/iio/adc/mxs-lradc.c b/drivers/staging/iio/adc/mxs-lradc.c
index 37a1192f1637..57563571c965 100644
--- a/drivers/staging/iio/adc/mxs-lradc.c
+++ b/drivers/staging/iio/adc/mxs-lradc.c
@@ -917,11 +917,12 @@ 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;
 		}
--
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