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iio: tmag5273: fix temperature offset

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The current offset has the scale already applied to it. The ABI
documentation defines the offset parameter as "offset to be added
to <type>[Y]_raw prior to scaling by <type>[Y]_scale in order to
obtain value in the <type> units as specified in <type>[Y]_raw
documentation"

The right value is obtained at 0 degrees Celsius by the formula provided
in the datasheet:

T = Tsens_t0 + (Tadc_t - Tadc_t0) / Tadc_res

where:
T = 0 degrees Celsius
Tsens_t0 (reference temperature) = 25 degrees Celsius
Tadc_t0 (16-bit format for Tsens_t0) = 17508
Tadc_res = 60.1 LSB/degree Celsius

The resulting offset is 16005.5, which has been truncated to 16005 to
provide an integer value with a precision loss smaller than the 1-LSB
measurement precision.

Fix the offset to apply its value prior to scaling.

Signed-off-by: Javier Carrasco <javier.carrasco@wolfvision.net>
Link: https://lore.kernel.org/r/9879beec-05fc-4fc6-af62-d771e238954e@wolfvision.net
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
This commit is contained in:
Javier Carrasco 2023-11-21 06:48:39 +01:00 committed by Jonathan Cameron
parent 54cf39ec16
commit 3b8157ec45
1 changed files with 1 additions and 1 deletions
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2
drivers/iio/magnetometer/tmag5273.c
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@ -356,7 +356,7 @@ static int tmag5273_read_raw(struct iio_dev *indio_dev,
case IIO_CHAN_INFO_OFFSET:
switch (chan->type) {
case IIO_TEMP:
*val = -266314;
*val = -16005;
return IIO_VAL_INT;
default:
return -EINVAL;