linux-kernel - [PATCH v3 05/13] iio: pressure: mprls0025pa: fix pressure calculation

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Message-Id: <20260114-mprls_cleanup-v3-5-bc7f1c2957c2@subdimension.ro>
Date: Wed, 14 Jan 2026 18:55:34 +0200
From: Petre Rodan <petre.rodan@...dimension.ro>
To: Jonathan Cameron <jic23@...nel.org>, 
 David Lechner <dlechner@...libre.com>, 
 Nuno Sá <nuno.sa@...log.com>, 
 Andy Shevchenko <andy@...nel.org>, Andreas Klinger <ak@...klinger.de>
Cc: linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Jonathan Cameron <Jonathan.Cameron@...wei.com>, 
 Petre Rodan <petre.rodan@...dimension.ro>
Subject: [PATCH v3 05/13] iio: pressure: mprls0025pa: fix pressure
 calculation

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@...dimension.ro>
---
v1 -> v2 slightly changed commit message, added fixes tag
v2 -> v3 reorder variables
---
 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 6ba45d4c16b3..d4133fef91fa 100644
--- a/drivers/iio/pressure/mprls0025pa.c
+++ b/drivers/iio/pressure/mprls0025pa.c
@@ -59,7 +59,7 @@
  *
  * 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)
  */
@@ -313,8 +313,7 @@ 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;
 	}
@@ -330,8 +329,9 @@ 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;
+	s64 odelta, pdelta;
 	u32 func;
+	s32 tmp;
 
 	indio_dev = devm_iio_device_alloc(dev, sizeof(*data));
 	if (!indio_dev)
@@ -405,17 +405,13 @@ 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, 0,
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