[PATCH v2] iio: mxs-lradc: Fix temperature offset

[PATCH v2] iio: mxs-lradc: Fix temperature offset

[Alexandre Belloni]

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>
---
 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 3f7715c9968b..47fc00a3f63b 100644
--- a/drivers/staging/iio/adc/mxs-lradc.c
+++ b/drivers/staging/iio/adc/mxs-lradc.c
@@ -915,11 +915,12 @@ 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;
 		}
-- 
2.1.4

Re: [PATCH v2] iio: mxs-lradc: Fix temperature offset

[Stefan Wahren]

Am 07.10.2015 um 13:10 schrieb Alexandre Belloni:
> 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>

Thanks

Re: [PATCH v2] iio: mxs-lradc: Fix temperature offset

[Jonathan Cameron]

On 07/10/15 16:07, Stefan Wahren wrote:
> Am 07.10.2015 um 13:10 schrieb Alexandre Belloni:
>> 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>
Applied to the fixes-togreg branch of iio.git and
marked for stable.

Thanks,

Jonathan
> 
> Thanks
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