linux-kernel - [PATCH 3.19.y-ckt 026/196] iio: pressure: mpl115: fix temperature offset sign

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Message-Id: <1457483454-30115-27-git-send-email-kamal@canonical.com>
Date:	Tue,  8 Mar 2016 16:28:04 -0800
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Akinobu Mita <akinobu.mita@...il.com>,
	Jonathan Cameron <jic23@...nel.org>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.19.y-ckt 026/196] iio: pressure: mpl115: fix temperature offset sign

3.19.8-ckt16 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Akinobu Mita <akinobu.mita@...il.com>

commit 431386e783a3a6c8b7707bee32d18c353b8688b2 upstream.

According to the datasheet, the resolusion of temperature sensor is
-5.35 counts/C. Temperature ADC is 472 counts at 25C.
(https://www.sparkfun.com/datasheets/Sensors/Pressure/MPL115A1.pdf
NOTE: This is older revision, but this information is removed from the
latest datasheet from nxp somehow)

Temp [C] = (Tadc - 472) / -5.35 + 25
         = (Tadc - 605.750000) * -0.186915888

So the correct offset is -605.750000.

Signed-off-by: Akinobu Mita <akinobu.mita@...il.com>
Acked-by: Peter Meerwald-Stadler <pmeerw@...erw.net>
Signed-off-by: Jonathan Cameron <jic23@...nel.org>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 drivers/iio/pressure/mpl115.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iio/pressure/mpl115.c b/drivers/iio/pressure/mpl115.c
index f5ecd6e..a0d7dee 100644
--- a/drivers/iio/pressure/mpl115.c
+++ b/drivers/iio/pressure/mpl115.c
@@ -117,7 +117,7 @@ static int mpl115_read_raw(struct iio_dev *indio_dev,
 		*val = ret >> 6;
 		return IIO_VAL_INT;
 	case IIO_CHAN_INFO_OFFSET:
-		*val = 605;
+		*val = -605;
 		*val2 = 750000;
 		return IIO_VAL_INT_PLUS_MICRO;
 	case IIO_CHAN_INFO_SCALE:
-- 
2.7.0