[PATCH v2 05/13] iio: pressure: mprls0025pa: fix pressure calculation

Petre Rodan
2026-01-14T10:07:52Z

A sign change is needed for proper calculation of the pressure.

This is a minor fix since it only affects users that might have custom
silicon from Honeywell that has honeywell,pmin-pascal != 0.

Also due to the fact that raw pressure values can not be lower
than output_min (400k-3.3M) there is no need to calculate a decimal for
the offset.

Fixes: 713337d9143e ("iio: pressure: Honeywell mprls0025pa pressure sensor")
Signed-off-by: Petre Rodan <petre.rodan@subdimension.ro>
---
v1 -> v2 slightly changed commit message, added fixes tag
---
drivers/iio/pressure/mprls0025pa.c | 26 +++++++++++---------------
drivers/iio/pressure/mprls0025pa.h | 2 --
2 files changed, 11 insertions(+), 17 deletions(-)

diff --git a/drivers/iio/pressure/mprls0025pa.c b/drivers/iio/pressure/mprls0025pa.c
index cec0bb3fc16f..2142df7932e8 100644
--- a/drivers/iio/pressure/mprls0025pa.c
+++ b/drivers/iio/pressure/mprls0025pa.c
@@ -60,7 +60,7 @@
*
* Values given to the userspace in sysfs interface:
* * raw - press_cnt
- * * offset - (-1 * outputmin) - pmin / scale
+ * * offset - (-1 * outputmin) + pmin / scale
* note: With all sensors from the datasheet pmin = 0
* which reduces the offset to (-1 * outputmin)
*/
@@ -314,8 +314,7 @@ static int mpr_read_raw(struct iio_dev *indio_dev,
return IIO_VAL_INT_PLUS_NANO;
case IIO_CHAN_INFO_OFFSET:
*val = data->offset;
- *val2 = data->offset2;
- return IIO_VAL_INT_PLUS_NANO;
+ return IIO_VAL_INT;
default:
return -EINVAL;
}
@@ -331,8 +330,9 @@ int mpr_common_probe(struct device *dev, const struct mpr_ops *ops, int irq)
struct mpr_data *data;
struct iio_dev *indio_dev;
const char *triplet;
- s64 scale, offset;
u32 func;
+ s32 tmp;
+ s64 odelta, pdelta;

indio_dev = devm_iio_device_alloc(dev, sizeof(*data));
if (!indio_dev)
@@ -406,17 +406,13 @@ int mpr_common_probe(struct device *dev, const struct mpr_ops *ops, int irq)
data->outmin = mpr_func_spec[data->function].output_min;
data->outmax = mpr_func_spec[data->function].output_max;

- /* use 64 bit calculation for preserving a reasonable precision */
- scale = div_s64(((s64)(data->pmax - data->pmin)) * NANO,
- data->outmax - data->outmin);
- data->scale = div_s64_rem(scale, NANO, &data->scale2);
- /*
- * multiply with NANO before dividing by scale and later divide by NANO
- * again.
- */
- offset = ((-1LL) * (s64)data->outmin) * NANO -
- div_s64(div_s64((s64)data->pmin * NANO, scale), NANO);
- data->offset = div_s64_rem(offset, NANO, &data->offset2);
+ odelta = data->outmax - data->outmin;
+ pdelta = data->pmax - data->pmin;
+
+ data->scale = div_s64_rem(div_s64(pdelta * NANO, odelta), NANO, &tmp);
+ data->scale2 = tmp;
+
+ data->offset = div_s64(odelta * data->pmin, pdelta) - data->outmin;

if (data->irq > 0) {
ret = devm_request_irq(dev, data->irq, mpr_eoc_handler,
diff --git a/drivers/iio/pressure/mprls0025pa.h b/drivers/iio/pressure/mprls0025pa.h
index d62a018eaff3..b6944b305126 100644
--- a/drivers/iio/pressure/mprls0025pa.h
+++ b/drivers/iio/pressure/mprls0025pa.h
@@ -53,7 +53,6 @@ enum mpr_func_id {
* @scale: pressure scale
* @scale2: pressure scale, decimal number
* @offset: pressure offset
- * @offset2: pressure offset, decimal number
* @gpiod_reset: reset
* @irq: end of conversion irq. used to distinguish between irq mode and
* reading in a loop until data is ready
@@ -75,7 +74,6 @@ struct mpr_data {
int scale;
int scale2;
int offset;
- int offset2;
struct gpio_desc *gpiod_reset;
int irq;
struct completion completion;

--
2.52.0