linux-kernel - [PATCH 10/14] iio: pressure: mprls0025pa: cleanup pressure calculation

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Message-Id: <20251218-mprls_cleanup-v1-10-b36a170f1a5c@subdimension.ro>
Date: Thu, 18 Dec 2025 13:05:52 +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>
Subject: [PATCH 10/14] iio: pressure: mprls0025pa: cleanup pressure
 calculation

A sign change is needed for proper calculation of the pressure.
The value of the affected element is zero for all official MPR sensors
covered in the datasheet.

The change will however ensure a correct calculation if a custom chip
is used (and if honeywell,pmin-pascal != 0 in the device tree overlay).

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.

Signed-off-by: Petre Rodan <petre.rodan@...dimension.ro>
---
 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 a1d7ec358036..9b18d5fb7e42 100644
--- a/drivers/iio/pressure/mprls0025pa.c
+++ b/drivers/iio/pressure/mprls0025pa.c
@@ -64,7 +64,7 @@
  *
  * 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)
  */
@@ -307,8 +307,7 @@ 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;
 	}
@@ -324,8 +323,9 @@ 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)
@@ -394,17 +394,13 @@ 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 50c99ddc8937..2bdffe1e0eb1 100644
--- a/drivers/iio/pressure/mprls0025pa.h
+++ b/drivers/iio/pressure/mprls0025pa.h
@@ -47,7 +47,6 @@ 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
@@ -69,7 +68,6 @@ struct mpr_data {
 	int			scale;
 	int			scale2;
 	int			offset;
-	int			offset2;
 	struct gpio_desc	*gpiod_reset;
 	int			irq;
 	struct completion	completion;

-- 
2.51.2