[PATCH v14 00/11] iio: afe: add temperature rescaling support

[PATCH v14 00/11] iio: afe: add temperature rescaling support

[Liam Beguin]

Jonathan, Peter, Andy,

This series focuses on adding temperature rescaling support to the IIO
Analog Front End (AFE) driver.

The first few patches from previous iterations addressing minor bugs in
IIO inkernel functions have been taken in, and are no longer in v13.

The main changes to the AFE driver include an initial Kunit test suite,
support for IIO_VAL_INT_PLUS_{NANO,MICRO} scales, and support for RTDs
and temperature transducer sensors.

I'm not quite sure what happened with the left-shift change last time,
I had it in my v12 local branch, it seems I got mixed up before sending.

Thanks for your time,
Liam

Changes since v13:
- fix SI prefix in rescale_temp_sense_rtd_props()
- add comment explaining SI prefixes are sometimes used as mathematical
  multipliers with no particular physical meaning associated.

Changes since v12:
- rebase on latest testing branch
- fix copyright holder in newly created header file
- add myself as a copyright holder of the iio-rescale.c driver at
  Peter's suggestion
- fix undefined behavior on left-shift operation

Changes since v11:
- update commits with my personal email since all this work was done on
  my own time
- apply Peter's Reviewed-by to my local tree
- fix use of units.h
- make use of units.h more consistently in iio-rescale.c and in the
  tests
- fix #include ordering
- treat 04/16 as a fix. Move it, and add a Fixes: tag
- fix undefined behavior on left-shift operation
- add comment about fract_mult with iio_str_to_fixpoint()
- reword commit message for 14/16, based on Andy's comments

Changes since v10:
- apply Andy's suggestion for offset calculations
- make use of units.h more consistently

Changes since v9:
- make use of linux/units.h
- reorder commits, fix fract_log2 before merging fract
- keep fractional representation when not overflowing

Changes since v8:
- reword comment
- fix erroneous 64-bit division
- optimize and use 32-bit divisions when values are know to not overflow
- keep IIO_VAL_FRACTIONAL scale when possible, if not default to fixed
  point
- add test cases
- use nano precision in test cases
- simplify offset calculation in rtd_props()

Changes since v7:
- drop gcd() logic in rescale_process_scale()
- use div_s64() instead of do_div() for signed 64-bit divisions
- combine IIO_VAL_FRACTIONAL and IIO_VAL_FRACTIONAL_LOG2 scale cases
- switch to INT_PLUS_NANO when accuracy is lost with FRACTIONAL scales
- rework test logic to allow for small relative error
- rename test variables to align error output messages

Changes since v6:
- rework IIO_VAL_INT_PLUS_{NANO,MICRO} based on Peter's suggestion
- combine IIO_VAL_INT_PLUS_{NANO,MICRO} cases
- add test cases for negative IIO_VAL_INT_PLUS_{NANO,MICRO} corner cases
- force use of positive integers with gcd()
- reduce risk of integer overflow in IIO_VAL_FRACTIONAL_LOG2
- fix duplicate symbol build error
- apply Reviewed-by

Changes since v5:
- add include/linux/iio/afe/rescale.h
- expose functions use to process scale and offset
- add basic iio-rescale kunit test cases
- fix integer overflow case
- improve precision for IIO_VAL_FRACTIONAL_LOG2

Changes since v4:
- only use gcd() when necessary in overflow mitigation
- fix INT_PLUS_{MICRO,NANO} support
- apply Reviewed-by
- fix temperature-transducer bindings

Changes since v3:
- drop unnecessary fallthrough statements
- drop redundant local variables in some calculations
- fix s64 divisions on 32bit platforms by using do_div
- add comment describing iio-rescaler offset calculation
- drop unnecessary MAINTAINERS entry

Changes since v2:
- don't break implicit offset truncations
- make a best effort to get a valid value for fractional types
- drop return value change in iio_convert_raw_to_processed_unlocked()
- don't rely on processed value for offset calculation
- add INT_PLUS_{MICRO,NANO} support in iio-rescale
- revert generic implementation in favor of temperature-sense-rtd and
  temperature-transducer
- add separate section to MAINTAINERS file

Changes since v1:
- rebase on latest iio `testing` branch
- also apply consumer scale on integer channel scale types
- don't break implicit truncation in processed channel offset
  calculation
- drop temperature AFE flavors in favor of a simpler generic
  implementation

Liam Beguin (11):
  iio: afe: rescale: expose scale processing function
  iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support
  iio: afe: rescale: add offset support
  iio: afe: rescale: fix accuracy for small fractional scales
  iio: afe: rescale: reduce risk of integer overflow
  iio: afe: rescale: make use of units.h
  iio: test: add basic tests for the iio-rescale driver
  iio: afe: rescale: add RTD temperature sensor support
  iio: afe: rescale: add temperature transducers
  dt-bindings: iio: afe: add bindings for temperature-sense-rtd
  dt-bindings: iio: afe: add bindings for temperature transducers

 .../iio/afe/temperature-sense-rtd.yaml        | 101 +++
 .../iio/afe/temperature-transducer.yaml       | 114 +++
 drivers/iio/afe/iio-rescale.c                 | 297 +++++++-
 drivers/iio/test/Kconfig                      |  10 +
 drivers/iio/test/Makefile                     |   1 +
 drivers/iio/test/iio-test-rescale.c           | 711 ++++++++++++++++++
 include/linux/iio/afe/rescale.h               |  36 +
 7 files changed, 1231 insertions(+), 39 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml
 create mode 100644 Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml
 create mode 100644 drivers/iio/test/iio-test-rescale.c
 create mode 100644 include/linux/iio/afe/rescale.h

Range-diff against v13:
 -:  ------------ >  1:  ee26b0eeac65 iio: afe: rescale: expose scale processing function
 -:  ------------ >  2:  a510097c83f1 iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support
 -:  ------------ >  3:  8f2f2699a9b4 iio: afe: rescale: add offset support
 -:  ------------ >  4:  2efa970bad26 iio: afe: rescale: fix accuracy for small fractional scales
 -:  ------------ >  5:  201037c0ead8 iio: afe: rescale: reduce risk of integer overflow
 1:  0e3bf50d9eb2 !  6:  a0037cc3ee90 iio: afe: rescale: make use of units.h
    @@ drivers/iio/afe/iio-rescale.c: int rescale_process_scale(struct rescale *rescale
      		fallthrough;
      	case IIO_VAL_FRACTIONAL_LOG2:
     -		tmp = (s64)*val * 1000000000LL;
    ++		/*
    ++		 * GIGA is used here as an arbitrarily large multiplier to avoid
    ++		 * precision loss in the division. It doesn't have any physical
    ++		 * meaning attached to it.
    ++		 */
     +		tmp = (s64)*val * GIGA;
      		tmp = div_s64(tmp, rescale->denominator);
      		tmp *= rescale->numerator;
 2:  72813d9788e4 =  7:  f8d47728f482 iio: test: add basic tests for the iio-rescale driver
 3:  8ee4c16355af !  8:  a04685586340 iio: afe: rescale: add RTD temperature sensor support
    @@ drivers/iio/afe/iio-rescale.c: static int rescale_voltage_divider_props(struct d
     +	rescale->numerator = MEGA / factor;
     +	rescale->denominator = tmp / factor;
     +
    -+	rescale->offset = -1 * ((r0 * iexc) / MEGA * MILLI);
    ++	rescale->offset = -1 * ((r0 * iexc) / KILO);
     +
     +	return 0;
     +}
 4:  36a9bb066369 =  9:  e3b716aaee50 iio: afe: rescale: add temperature transducers
 5:  581962b44cf3 = 10:  22ae1458eb8b dt-bindings: iio: afe: add bindings for temperature-sense-rtd
 6:  d09d377b05ac = 11:  33825ad452d6 dt-bindings: iio: afe: add bindings for temperature transducers

base-commit: cd717ac6f69db4953ca701c6220c7cb58e17f35a
-- 
2.35.1.4.g5d01301f2b86

[PATCH v14 01/11] iio: afe: rescale: expose scale processing function

[Liam Beguin]

In preparation for the addition of kunit tests, expose the logic
responsible for combining channel scales.

Signed-off-by: Liam Beguin <liambeguin@gmail.com>
Reviewed-by: Peter Rosin <peda@axentia.se>
---
 drivers/iio/afe/iio-rescale.c   | 65 ++++++++++++++-------------------
 include/linux/iio/afe/rescale.h | 32 ++++++++++++++++
 2 files changed, 60 insertions(+), 37 deletions(-)
 create mode 100644 include/linux/iio/afe/rescale.h

diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
index 69710c481376..65832dd09249 100644
--- a/drivers/iio/afe/iio-rescale.c
+++ b/drivers/iio/afe/iio-rescale.c
@@ -15,32 +15,43 @@
 #include <linux/platform_device.h>
 #include <linux/property.h>
 
+#include <linux/iio/afe/rescale.h>
 #include <linux/iio/consumer.h>
 #include <linux/iio/iio.h>
 
-struct rescale;
-
-struct rescale_cfg {
-	enum iio_chan_type type;
-	int (*props)(struct device *dev, struct rescale *rescale);
-};
+int rescale_process_scale(struct rescale *rescale, int scale_type,
+			  int *val, int *val2)
+{
+	s64 tmp;
 
-struct rescale {
-	const struct rescale_cfg *cfg;
-	struct iio_channel *source;
-	struct iio_chan_spec chan;
-	struct iio_chan_spec_ext_info *ext_info;
-	bool chan_processed;
-	s32 numerator;
-	s32 denominator;
-};
+	switch (scale_type) {
+	case IIO_VAL_FRACTIONAL:
+		*val *= rescale->numerator;
+		*val2 *= rescale->denominator;
+		return scale_type;
+	case IIO_VAL_INT:
+		*val *= rescale->numerator;
+		if (rescale->denominator == 1)
+			return scale_type;
+		*val2 = rescale->denominator;
+		return IIO_VAL_FRACTIONAL;
+	case IIO_VAL_FRACTIONAL_LOG2:
+		tmp = (s64)*val * 1000000000LL;
+		tmp = div_s64(tmp, rescale->denominator);
+		tmp *= rescale->numerator;
+		tmp = div_s64(tmp, 1000000000LL);
+		*val = tmp;
+		return scale_type;
+	default:
+		return -EOPNOTSUPP;
+	}
+}
 
 static int rescale_read_raw(struct iio_dev *indio_dev,
 			    struct iio_chan_spec const *chan,
 			    int *val, int *val2, long mask)
 {
 	struct rescale *rescale = iio_priv(indio_dev);
-	s64 tmp;
 	int ret;
 
 	switch (mask) {
@@ -66,27 +77,7 @@ static int rescale_read_raw(struct iio_dev *indio_dev,
 		} else {
 			ret = iio_read_channel_scale(rescale->source, val, val2);
 		}
-		switch (ret) {
-		case IIO_VAL_FRACTIONAL:
-			*val *= rescale->numerator;
-			*val2 *= rescale->denominator;
-			return ret;
-		case IIO_VAL_INT:
-			*val *= rescale->numerator;
-			if (rescale->denominator == 1)
-				return ret;
-			*val2 = rescale->denominator;
-			return IIO_VAL_FRACTIONAL;
-		case IIO_VAL_FRACTIONAL_LOG2:
-			tmp = (s64)*val * 1000000000LL;
-			tmp = div_s64(tmp, rescale->denominator);
-			tmp *= rescale->numerator;
-			tmp = div_s64(tmp, 1000000000LL);
-			*val = tmp;
-			return ret;
-		default:
-			return -EOPNOTSUPP;
-		}
+		return rescale_process_scale(rescale, ret, val, val2);
 	default:
 		return -EINVAL;
 	}
diff --git a/include/linux/iio/afe/rescale.h b/include/linux/iio/afe/rescale.h
new file mode 100644
index 000000000000..8a2eb34af327
--- /dev/null
+++ b/include/linux/iio/afe/rescale.h
@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2018 Axentia Technologies AB
+ */
+
+#ifndef __IIO_RESCALE_H__
+#define __IIO_RESCALE_H__
+
+#include <linux/types.h>
+#include <linux/iio/iio.h>
+
+struct device;
+struct rescale;
+
+struct rescale_cfg {
+	enum iio_chan_type type;
+	int (*props)(struct device *dev, struct rescale *rescale);
+};
+
+struct rescale {
+	const struct rescale_cfg *cfg;
+	struct iio_channel *source;
+	struct iio_chan_spec chan;
+	struct iio_chan_spec_ext_info *ext_info;
+	bool chan_processed;
+	s32 numerator;
+	s32 denominator;
+};
+
+int rescale_process_scale(struct rescale *rescale, int scale_type,
+			  int *val, int *val2);
+#endif /* __IIO_RESCALE_H__ */
-- 
2.35.1.4.g5d01301f2b86

[PATCH v14 02/11] iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support

[Liam Beguin]

Some ADCs use IIO_VAL_INT_PLUS_{NANO,MICRO} scale types.
Add support for these to allow using the iio-rescaler with them.

Signed-off-by: Liam Beguin <liambeguin@gmail.com>
Reviewed-by: Peter Rosin <peda@axentia.se>
---
 drivers/iio/afe/iio-rescale.c | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
index 65832dd09249..f833eb38f8bb 100644
--- a/drivers/iio/afe/iio-rescale.c
+++ b/drivers/iio/afe/iio-rescale.c
@@ -14,6 +14,7 @@
 #include <linux/of_device.h>
 #include <linux/platform_device.h>
 #include <linux/property.h>
+#include <linux/units.h>
 
 #include <linux/iio/afe/rescale.h>
 #include <linux/iio/consumer.h>
@@ -23,6 +24,9 @@ int rescale_process_scale(struct rescale *rescale, int scale_type,
 			  int *val, int *val2)
 {
 	s64 tmp;
+	s32 rem;
+	u32 mult;
+	u32 neg;
 
 	switch (scale_type) {
 	case IIO_VAL_FRACTIONAL:
@@ -41,6 +45,37 @@ int rescale_process_scale(struct rescale *rescale, int scale_type,
 		tmp *= rescale->numerator;
 		tmp = div_s64(tmp, 1000000000LL);
 		*val = tmp;
+		return scale_type;
+	case IIO_VAL_INT_PLUS_NANO:
+	case IIO_VAL_INT_PLUS_MICRO:
+		mult = scale_type == IIO_VAL_INT_PLUS_NANO ? GIGA : MEGA;
+
+		/*
+		 * For IIO_VAL_INT_PLUS_{MICRO,NANO} scale types if either *val
+		 * OR *val2 is negative the schan scale is negative, i.e.
+		 * *val = 1 and *val2 = -0.5 yields -1.5 not -0.5.
+		 */
+		neg = *val < 0 || *val2 < 0;
+
+		tmp = (s64)abs(*val) * abs(rescale->numerator);
+		*val = div_s64_rem(tmp, abs(rescale->denominator), &rem);
+
+		tmp = (s64)rem * mult + (s64)abs(*val2) * abs(rescale->numerator);
+		tmp = div_s64(tmp, abs(rescale->denominator));
+
+		*val += div_s64_rem(tmp, mult, val2);
+
+		/*
+		 * If only one of the rescaler elements or the schan scale is
+		 * negative, the combined scale is negative.
+		 */
+		if (neg ^ ((rescale->numerator < 0) ^ (rescale->denominator < 0))) {
+			if (*val)
+				*val = -*val;
+			else
+				*val2 = -*val2;
+		}
+
 		return scale_type;
 	default:
 		return -EOPNOTSUPP;
-- 
2.35.1.4.g5d01301f2b86

[PATCH v14 03/11] iio: afe: rescale: add offset support

[Liam Beguin]

This is a preparatory change required for the addition of temperature
sensing front ends.

Signed-off-by: Liam Beguin <liambeguin@gmail.com>
Reviewed-by: Peter Rosin <peda@axentia.se>
---
 drivers/iio/afe/iio-rescale.c   | 81 +++++++++++++++++++++++++++++++++
 include/linux/iio/afe/rescale.h |  4 ++
 2 files changed, 85 insertions(+)

diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
index f833eb38f8bb..63035b4bce5e 100644
--- a/drivers/iio/afe/iio-rescale.c
+++ b/drivers/iio/afe/iio-rescale.c
@@ -3,6 +3,7 @@
  * IIO rescale driver
  *
  * Copyright (C) 2018 Axentia Technologies AB
+ * Copyright (C) 2022 Liam Beguin <liambeguin@gmail.com>
  *
  * Author: Peter Rosin <peda@axentia.se>
  */
@@ -82,11 +83,46 @@ int rescale_process_scale(struct rescale *rescale, int scale_type,
 	}
 }
 
+int rescale_process_offset(struct rescale *rescale, int scale_type,
+			   int scale, int scale2, int schan_off,
+			   int *val, int *val2)
+{
+	s64 tmp, tmp2;
+
+	switch (scale_type) {
+	case IIO_VAL_FRACTIONAL:
+		tmp = (s64)rescale->offset * scale2;
+		*val = div_s64(tmp, scale) + schan_off;
+		return IIO_VAL_INT;
+	case IIO_VAL_INT:
+		*val = div_s64(rescale->offset, scale) + schan_off;
+		return IIO_VAL_INT;
+	case IIO_VAL_FRACTIONAL_LOG2:
+		tmp = (s64)rescale->offset * (1 << scale2);
+		*val = div_s64(tmp, scale) + schan_off;
+		return IIO_VAL_INT;
+	case IIO_VAL_INT_PLUS_NANO:
+		tmp = (s64)rescale->offset * GIGA;
+		tmp2 = ((s64)scale * GIGA) + scale2;
+		*val = div64_s64(tmp, tmp2) + schan_off;
+		return IIO_VAL_INT;
+	case IIO_VAL_INT_PLUS_MICRO:
+		tmp = (s64)rescale->offset * MEGA;
+		tmp2 = ((s64)scale * MEGA) + scale2;
+		*val = div64_s64(tmp, tmp2) + schan_off;
+		return IIO_VAL_INT;
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+
 static int rescale_read_raw(struct iio_dev *indio_dev,
 			    struct iio_chan_spec const *chan,
 			    int *val, int *val2, long mask)
 {
 	struct rescale *rescale = iio_priv(indio_dev);
+	int scale, scale2;
+	int schan_off = 0;
 	int ret;
 
 	switch (mask) {
@@ -113,6 +149,47 @@ static int rescale_read_raw(struct iio_dev *indio_dev,
 			ret = iio_read_channel_scale(rescale->source, val, val2);
 		}
 		return rescale_process_scale(rescale, ret, val, val2);
+	case IIO_CHAN_INFO_OFFSET:
+		/*
+		 * Processed channels are scaled 1-to-1 and source offset is
+		 * already taken into account.
+		 *
+		 * In other cases, real world measurement are expressed as:
+		 *
+		 *	schan_scale * (raw + schan_offset)
+		 *
+		 * Given that the rescaler parameters are applied recursively:
+		 *
+		 *	rescaler_scale * (schan_scale * (raw + schan_offset) +
+		 *		rescaler_offset)
+		 *
+		 * Or,
+		 *
+		 *	(rescaler_scale * schan_scale) * (raw +
+		 *		(schan_offset +	rescaler_offset / schan_scale)
+		 *
+		 * Thus, reusing the original expression the parameters exposed
+		 * to userspace are:
+		 *
+		 *	scale = schan_scale * rescaler_scale
+		 *	offset = schan_offset + rescaler_offset / schan_scale
+		 */
+		if (rescale->chan_processed) {
+			*val = rescale->offset;
+			return IIO_VAL_INT;
+		}
+
+		if (iio_channel_has_info(rescale->source->channel,
+					 IIO_CHAN_INFO_OFFSET)) {
+			ret = iio_read_channel_offset(rescale->source,
+						      &schan_off, NULL);
+			if (ret != IIO_VAL_INT)
+				return ret < 0 ? ret : -EOPNOTSUPP;
+		}
+
+		ret = iio_read_channel_scale(rescale->source, &scale, &scale2);
+		return rescale_process_offset(rescale, ret, scale, scale2,
+					      schan_off, val, val2);
 	default:
 		return -EINVAL;
 	}
@@ -189,6 +266,9 @@ static int rescale_configure_channel(struct device *dev,
 	chan->info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
 		BIT(IIO_CHAN_INFO_SCALE);
 
+	if (rescale->offset)
+		chan->info_mask_separate |= BIT(IIO_CHAN_INFO_OFFSET);
+
 	/*
 	 * Using .read_avail() is fringe to begin with and makes no sense
 	 * whatsoever for processed channels, so we make sure that this cannot
@@ -353,6 +433,7 @@ static int rescale_probe(struct platform_device *pdev)
 	rescale->cfg = of_device_get_match_data(dev);
 	rescale->numerator = 1;
 	rescale->denominator = 1;
+	rescale->offset = 0;
 
 	ret = rescale->cfg->props(dev, rescale);
 	if (ret)
diff --git a/include/linux/iio/afe/rescale.h b/include/linux/iio/afe/rescale.h
index 8a2eb34af327..6eecb435488f 100644
--- a/include/linux/iio/afe/rescale.h
+++ b/include/linux/iio/afe/rescale.h
@@ -25,8 +25,12 @@ struct rescale {
 	bool chan_processed;
 	s32 numerator;
 	s32 denominator;
+	s32 offset;
 };
 
 int rescale_process_scale(struct rescale *rescale, int scale_type,
 			  int *val, int *val2);
+int rescale_process_offset(struct rescale *rescale, int scale_type,
+			   int scale, int scale2, int schan_off,
+			   int *val, int *val2);
 #endif /* __IIO_RESCALE_H__ */
-- 
2.35.1.4.g5d01301f2b86

[PATCH v14 04/11] iio: afe: rescale: fix accuracy for small fractional scales

[Liam Beguin]

The approximation caused by integer divisions can be costly on smaller
scale values since the decimal part is significant compared to the
integer part. Switch to an IIO_VAL_INT_PLUS_NANO scale type in such
cases to maintain accuracy.

Signed-off-by: Liam Beguin <liambeguin@gmail.com>
Reviewed-by: Peter Rosin <peda@axentia.se>
---
 drivers/iio/afe/iio-rescale.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
index 63035b4bce5e..468e6c345bd1 100644
--- a/drivers/iio/afe/iio-rescale.c
+++ b/drivers/iio/afe/iio-rescale.c
@@ -25,7 +25,7 @@ int rescale_process_scale(struct rescale *rescale, int scale_type,
 			  int *val, int *val2)
 {
 	s64 tmp;
-	s32 rem;
+	s32 rem, rem2;
 	u32 mult;
 	u32 neg;
 
@@ -44,9 +44,23 @@ int rescale_process_scale(struct rescale *rescale, int scale_type,
 		tmp = (s64)*val * 1000000000LL;
 		tmp = div_s64(tmp, rescale->denominator);
 		tmp *= rescale->numerator;
-		tmp = div_s64(tmp, 1000000000LL);
+
+		tmp = div_s64_rem(tmp, 1000000000LL, &rem);
 		*val = tmp;
-		return scale_type;
+
+		if (!rem)
+			return scale_type;
+
+		tmp = 1 << *val2;
+
+		rem2 = *val % (int)tmp;
+		*val = *val / (int)tmp;
+
+		*val2 = rem / (int)tmp;
+		if (rem2)
+			*val2 += div_s64((s64)rem2 * 1000000000LL, tmp);
+
+		return IIO_VAL_INT_PLUS_NANO;
 	case IIO_VAL_INT_PLUS_NANO:
 	case IIO_VAL_INT_PLUS_MICRO:
 		mult = scale_type == IIO_VAL_INT_PLUS_NANO ? GIGA : MEGA;
-- 
2.35.1.4.g5d01301f2b86

[PATCH v14 05/11] iio: afe: rescale: reduce risk of integer overflow

[Liam Beguin]

Reduce the risk of integer overflow by doing the scale calculation on
a 64-bit integer. Since the rescaling is only performed on *val, reuse
the IIO_VAL_FRACTIONAL_LOG2 case.

Signed-off-by: Liam Beguin <liambeguin@gmail.com>
Reviewed-by: Peter Rosin <peda@axentia.se>
---
 drivers/iio/afe/iio-rescale.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
index 468e6c345bd1..67273de46843 100644
--- a/drivers/iio/afe/iio-rescale.c
+++ b/drivers/iio/afe/iio-rescale.c
@@ -25,21 +25,31 @@ int rescale_process_scale(struct rescale *rescale, int scale_type,
 			  int *val, int *val2)
 {
 	s64 tmp;
+	int _val, _val2;
 	s32 rem, rem2;
 	u32 mult;
 	u32 neg;
 
 	switch (scale_type) {
-	case IIO_VAL_FRACTIONAL:
-		*val *= rescale->numerator;
-		*val2 *= rescale->denominator;
-		return scale_type;
 	case IIO_VAL_INT:
 		*val *= rescale->numerator;
 		if (rescale->denominator == 1)
 			return scale_type;
 		*val2 = rescale->denominator;
 		return IIO_VAL_FRACTIONAL;
+	case IIO_VAL_FRACTIONAL:
+		/*
+		 * When the product of both scales doesn't overflow, avoid
+		 * potential accuracy loss (for in kernel consumers) by
+		 * keeping a fractional representation.
+		 */
+		if (!check_mul_overflow(*val, rescale->numerator, &_val) &&
+		    !check_mul_overflow(*val2, rescale->denominator, &_val2)) {
+			*val = _val;
+			*val2 = _val2;
+			return IIO_VAL_FRACTIONAL;
+		}
+		fallthrough;
 	case IIO_VAL_FRACTIONAL_LOG2:
 		tmp = (s64)*val * 1000000000LL;
 		tmp = div_s64(tmp, rescale->denominator);
@@ -51,7 +61,10 @@ int rescale_process_scale(struct rescale *rescale, int scale_type,
 		if (!rem)
 			return scale_type;
 
-		tmp = 1 << *val2;
+		if (scale_type == IIO_VAL_FRACTIONAL)
+			tmp = *val2;
+		else
+			tmp = ULL(1) << *val2;
 
 		rem2 = *val % (int)tmp;
 		*val = *val / (int)tmp;
-- 
2.35.1.4.g5d01301f2b86

[PATCH v14 06/11] iio: afe: rescale: make use of units.h

[Liam Beguin]

Make use of well-defined SI metric prefixes to improve code readability.

Signed-off-by: Liam Beguin <liambeguin@gmail.com>
---
 drivers/iio/afe/iio-rescale.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
index 67273de46843..4601f84a83c2 100644
--- a/drivers/iio/afe/iio-rescale.c
+++ b/drivers/iio/afe/iio-rescale.c
@@ -51,11 +51,16 @@ int rescale_process_scale(struct rescale *rescale, int scale_type,
 		}
 		fallthrough;
 	case IIO_VAL_FRACTIONAL_LOG2:
-		tmp = (s64)*val * 1000000000LL;
+		/*
+		 * GIGA is used here as an arbitrarily large multiplier to avoid
+		 * precision loss in the division. It doesn't have any physical
+		 * meaning attached to it.
+		 */
+		tmp = (s64)*val * GIGA;
 		tmp = div_s64(tmp, rescale->denominator);
 		tmp *= rescale->numerator;
 
-		tmp = div_s64_rem(tmp, 1000000000LL, &rem);
+		tmp = div_s64_rem(tmp, GIGA, &rem);
 		*val = tmp;
 
 		if (!rem)
@@ -71,7 +76,7 @@ int rescale_process_scale(struct rescale *rescale, int scale_type,
 
 		*val2 = rem / (int)tmp;
 		if (rem2)
-			*val2 += div_s64((s64)rem2 * 1000000000LL, tmp);
+			*val2 += div_s64((s64)rem2 * GIGA, tmp);
 
 		return IIO_VAL_INT_PLUS_NANO;
 	case IIO_VAL_INT_PLUS_NANO:
@@ -332,8 +337,8 @@ static int rescale_current_sense_amplifier_props(struct device *dev,
 	 * gain_div / (gain_mult * sense), while trying to keep the
 	 * numerator/denominator from overflowing.
 	 */
-	factor = gcd(sense, 1000000);
-	rescale->numerator = 1000000 / factor;
+	factor = gcd(sense, MEGA);
+	rescale->numerator = MEGA / factor;
 	rescale->denominator = sense / factor;
 
 	factor = gcd(rescale->numerator, gain_mult);
@@ -361,8 +366,8 @@ static int rescale_current_sense_shunt_props(struct device *dev,
 		return ret;
 	}
 
-	factor = gcd(shunt, 1000000);
-	rescale->numerator = 1000000 / factor;
+	factor = gcd(shunt, MEGA);
+	rescale->numerator = MEGA / factor;
 	rescale->denominator = shunt / factor;
 
 	return 0;
-- 
2.35.1.4.g5d01301f2b86

[PATCH v14 07/11] iio: test: add basic tests for the iio-rescale driver

[Liam Beguin]

The iio-rescale driver supports various combinations of scale types and
offsets. These can often result in large integer multiplications. Make
sure these calculations are done right by adding a set of kunit test
cases that build on top of iio-test-format.

To run these tests, add the following to .kunitconfig
	$ cat .kunitconfig
	CONFIG_IIO=y
	CONFIG_IIO_RESCALE_KUNIT_TEST=y
	CONFIG_KUNIT=y

Then run:
	$ ./tools/testing/kunit/kunit.py run --kunitconfig .kunitconfig

Signed-off-by: Liam Beguin <liambeguin@gmail.com>
Reviewed-by: Peter Rosin <peda@axentia.se>
---
 drivers/iio/test/Kconfig            |  10 +
 drivers/iio/test/Makefile           |   1 +
 drivers/iio/test/iio-test-rescale.c | 711 ++++++++++++++++++++++++++++
 3 files changed, 722 insertions(+)
 create mode 100644 drivers/iio/test/iio-test-rescale.c

diff --git a/drivers/iio/test/Kconfig b/drivers/iio/test/Kconfig
index 679a7794af20..872ed4ed140a 100644
--- a/drivers/iio/test/Kconfig
+++ b/drivers/iio/test/Kconfig
@@ -4,6 +4,16 @@
 #
 
 # Keep in alphabetical order
+config IIO_RESCALE_KUNIT_TEST
+	bool "Test IIO rescale conversion functions"
+	depends on KUNIT && !IIO_RESCALE
+	default KUNIT_ALL_TESTS
+	help
+	  If you want to run tests on the iio-rescale code say Y here.
+
+	  This takes advantage of ARCH=um to run tests and should be used by
+	  developers to tests their changes to the rescaling logic.
+
 config IIO_TEST_FORMAT
         bool "Test IIO formatting functions"
         depends on KUNIT=y
diff --git a/drivers/iio/test/Makefile b/drivers/iio/test/Makefile
index 467519a2027e..f15ae0a6394f 100644
--- a/drivers/iio/test/Makefile
+++ b/drivers/iio/test/Makefile
@@ -4,5 +4,6 @@
 #
 
 # Keep in alphabetical order
+obj-$(CONFIG_IIO_RESCALE_KUNIT_TEST) += iio-test-rescale.o ../afe/iio-rescale.o
 obj-$(CONFIG_IIO_TEST_FORMAT) += iio-test-format.o
 CFLAGS_iio-test-format.o += $(DISABLE_STRUCTLEAK_PLUGIN)
diff --git a/drivers/iio/test/iio-test-rescale.c b/drivers/iio/test/iio-test-rescale.c
new file mode 100644
index 000000000000..a3bbe2db76d3
--- /dev/null
+++ b/drivers/iio/test/iio-test-rescale.c
@@ -0,0 +1,711 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Kunit tests for IIO rescale conversions
+ *
+ * Copyright (c) 2021 Liam Beguin <liambeguin@gmail.com>
+ */
+
+#include <linux/gcd.h>
+#include <linux/overflow.h>
+#include <linux/units.h>
+
+#include <linux/iio/afe/rescale.h>
+#include <linux/iio/iio.h>
+
+#include <kunit/test.h>
+
+struct rescale_tc_data {
+	const char *name;
+
+	const s32 numerator;
+	const s32 denominator;
+	const s32 offset;
+
+	const int schan_val;
+	const int schan_val2;
+	const int schan_off;
+	const int schan_scale_type;
+
+	const char *expected;
+	const char *expected_off;
+};
+
+const struct rescale_tc_data scale_cases[] = {
+	/*
+	 * Typical use cases
+	 */
+	{
+		.name = "typical IIO_VAL_INT, positive",
+		.numerator = 1000000,
+		.denominator = 8060,
+		.schan_scale_type = IIO_VAL_INT,
+		.schan_val = 42,
+		.expected = "5210.918114143",
+	},
+	{
+		.name = "typical IIO_VAL_INT, negative",
+		.numerator = -1000000,
+		.denominator = 8060,
+		.schan_scale_type = IIO_VAL_INT,
+		.schan_val = 42,
+		.expected = "-5210.918114143",
+	},
+	{
+		.name = "typical IIO_VAL_FRACTIONAL, positive",
+		.numerator = 1000000,
+		.denominator = 8060,
+		.schan_scale_type = IIO_VAL_FRACTIONAL,
+		.schan_val = 42,
+		.schan_val2 = 20,
+		.expected = "260.545905707",
+	},
+	{
+		.name = "typical IIO_VAL_FRACTIONAL, negative",
+		.numerator = -1000000,
+		.denominator = 8060,
+		.schan_scale_type = IIO_VAL_FRACTIONAL,
+		.schan_val = 42,
+		.schan_val2 = 20,
+		.expected = "-260.545905707",
+	},
+	{
+		.name = "typical IIO_VAL_FRACTIONAL_LOG2, positive",
+		.numerator = 42,
+		.denominator = 53,
+		.schan_scale_type = IIO_VAL_FRACTIONAL_LOG2,
+		.schan_val = 4096,
+		.schan_val2 = 16,
+		.expected = "0.049528301",
+	},
+	{
+		.name = "typical IIO_VAL_FRACTIONAL_LOG2, negative",
+		.numerator = -42,
+		.denominator = 53,
+		.schan_scale_type = IIO_VAL_FRACTIONAL_LOG2,
+		.schan_val = 4096,
+		.schan_val2 = 16,
+		.expected = "-0.049528301",
+	},
+	{
+		.name = "typical IIO_VAL_INT_PLUS_NANO, positive",
+		.numerator = 1000000,
+		.denominator = 8060,
+		.schan_scale_type = IIO_VAL_INT_PLUS_NANO,
+		.schan_val = 10,
+		.schan_val2 = 123456,
+		.expected = "1240.710106203",
+	},
+	{
+		.name = "typical IIO_VAL_INT_PLUS_NANO, negative",
+		.numerator = -1000000,
+		.denominator = 8060,
+		.schan_scale_type = IIO_VAL_INT_PLUS_NANO,
+		.schan_val = 10,
+		.schan_val2 = 123456,
+		.expected = "-1240.710106203",
+	},
+	{
+		.name = "typical IIO_VAL_INT_PLUS_MICRO, positive",
+		.numerator = 1000000,
+		.denominator = 8060,
+		.schan_scale_type = IIO_VAL_INT_PLUS_MICRO,
+		.schan_val = 10,
+		.schan_val2 = 1234,
+		.expected = "1240.84789",
+	},
+	{
+		.name = "typical IIO_VAL_INT_PLUS_MICRO, negative",
+		.numerator = -1000000,
+		.denominator = 8060,
+		.schan_scale_type = IIO_VAL_INT_PLUS_MICRO,
+		.schan_val = 10,
+		.schan_val2 = 1234,
+		.expected = "-1240.84789",
+	},
+	/*
+	 * Use cases with small scales involving divisions
+	 */
+	{
+		.name = "small IIO_VAL_FRACTIONAL, 261/509 scaled by 90/1373754273",
+		.numerator = 261,
+		.denominator = 509,
+		.schan_scale_type = IIO_VAL_FRACTIONAL,
+		.schan_val = 90,
+		.schan_val2 = 1373754273,
+		.expected = "0.000000033594",
+	},
+	{
+		.name = "small IIO_VAL_FRACTIONAL, 90/1373754273 scaled by 261/509",
+		.numerator = 90,
+		.denominator = 1373754273,
+		.schan_scale_type = IIO_VAL_FRACTIONAL,
+		.schan_val = 261,
+		.schan_val2 = 509,
+		.expected = "0.000000033594",
+	},
+	{
+		.name = "small IIO_VAL_FRACTIONAL, 760/1373754273 scaled by 427/2727",
+		.numerator = 760,
+		.denominator = 1373754273,
+		.schan_scale_type = IIO_VAL_FRACTIONAL,
+		.schan_val = 427,
+		.schan_val2 = 2727,
+		.expected = "0.000000086626",
+	},
+	{
+		.name = "small IIO_VAL_FRACTIONAL, 761/1373754273 scaled by 427/2727",
+		.numerator = 761,
+		.denominator = 1373754273,
+		.schan_scale_type = IIO_VAL_FRACTIONAL,
+		.schan_val = 427,
+		.schan_val2 = 2727,
+		.expected = "0.000000086740",
+	},
+	{
+		.name = "small IIO_VAL_FRACTIONAL, 5/32768 scaled by 3/10000",
+		.numerator = 5,
+		.denominator = 32768,
+		.schan_scale_type = IIO_VAL_FRACTIONAL,
+		.schan_val = 3,
+		.schan_val2 = 10000,
+		.expected = "0.0000000457763671875",
+	},
+	{
+		.name = "small IIO_VAL_FRACTIONAL, 0 < scale < 1",
+		.numerator = 6,
+		.denominator = 6,
+		.schan_scale_type = IIO_VAL_FRACTIONAL,
+		.schan_val = 1,
+		.schan_val2 = 3,
+		.expected = "0.3333333333333333",
+	},
+	{
+		.name = "small IIO_VAL_FRACTIONAL, -1 < scale < 0",
+		.numerator = -6,
+		.denominator = 6,
+		.schan_scale_type = IIO_VAL_FRACTIONAL,
+		.schan_val = 1,
+		.schan_val2 = 3,
+		.expected = "-0.3333333333333333",
+	},
+	{
+		.name = "small IIO_VAL_FRACTIONAL, 0 < scale < 2",
+		.numerator = 8,
+		.denominator = 2,
+		.schan_scale_type = IIO_VAL_FRACTIONAL,
+		.schan_val = 1,
+		.schan_val2 = 3,
+		.expected = "1.3333333333333333",
+	},
+	{
+		.name = "small IIO_VAL_FRACTIONAL, -2 < scale < 0",
+		.numerator = -8,
+		.denominator = 2,
+		.schan_scale_type = IIO_VAL_FRACTIONAL,
+		.schan_val = 1,
+		.schan_val2 = 3,
+		.expected = "-1.3333333333333333",
+	},
+	{
+		.name = "small IIO_VAL_FRACTIONAL_LOG2, 760/32768 scaled by 15/22",
+		.numerator = 760,
+		.denominator = 32768,
+		.schan_scale_type = IIO_VAL_FRACTIONAL_LOG2,
+		.schan_val = 15,
+		.schan_val2 = 22,
+		.expected = "0.000000082946",
+	},
+	{
+		.name = "small IIO_VAL_FRACTIONAL_LOG2, 761/32768 scaled by 15/22",
+		.numerator = 761,
+		.denominator = 32768,
+		.schan_scale_type = IIO_VAL_FRACTIONAL_LOG2,
+		.schan_val = 15,
+		.schan_val2 = 22,
+		.expected = "0.000000083055",
+	},
+	{
+		.name = "small IIO_VAL_FRACTIONAL_LOG2, 0 < scale < 1",
+		.numerator = 16,
+		.denominator = 3,
+		.schan_scale_type = IIO_VAL_FRACTIONAL_LOG2,
+		.schan_val = 1,
+		.schan_val2 = 4,
+		.expected = "0.3333333333333333",
+	},
+	{
+		.name = "small IIO_VAL_FRACTIONAL_LOG2, -1 < scale < 0",
+		.numerator = -16,
+		.denominator = 3,
+		.schan_scale_type = IIO_VAL_FRACTIONAL_LOG2,
+		.schan_val = 1,
+		.schan_val2 = 4,
+		.expected = "-0.3333333333333333",
+	},
+	{
+		.name = "small IIO_VAL_FRACTIONAL_LOG2, 0 < scale < 2",
+		.numerator = 8,
+		.denominator = 3,
+		.schan_scale_type = IIO_VAL_FRACTIONAL_LOG2,
+		.schan_val = 1,
+		.schan_val2 = 1,
+		.expected = "1.3333333333333333",
+	},
+	{
+		.name = "small IIO_VAL_FRACTIONAL_LOG2, -2 < scale < 0",
+		.numerator = -8,
+		.denominator = 3,
+		.schan_scale_type = IIO_VAL_FRACTIONAL_LOG2,
+		.schan_val = 1,
+		.schan_val2 = 1,
+		.expected = "-1.3333333333333333",
+	},
+	{
+		.name = "small IIO_VAL_INT_PLUS_MICRO, positive",
+		.numerator = 1,
+		.denominator = 2,
+		.schan_scale_type = IIO_VAL_INT_PLUS_MICRO,
+		.schan_val = 5,
+		.schan_val2 = 1234,
+		.expected = "2.500617",
+	},
+	{
+		.name = "small IIO_VAL_INT_PLUS_MICRO, negative",
+		.numerator = -1,
+		.denominator = 2,
+		.schan_scale_type = IIO_VAL_INT_PLUS_MICRO,
+		.schan_val = 5,
+		.schan_val2 = 1234,
+		.expected = "-2.500617",
+	},
+	/*
+	 * INT_PLUS_{MICRO,NANO} positive/negative corner cases
+	 */
+	{
+		.name = "negative IIO_VAL_INT_PLUS_NANO, negative schan",
+		.numerator = 1000000,
+		.denominator = 8060,
+		.schan_scale_type = IIO_VAL_INT_PLUS_NANO,
+		.schan_val = -10,
+		.schan_val2 = 123456,
+		.expected = "-1240.710106203",
+	},
+	{
+		.name = "negative IIO_VAL_INT_PLUS_NANO, both negative",
+		.numerator = -1000000,
+		.denominator = 8060,
+		.schan_scale_type = IIO_VAL_INT_PLUS_NANO,
+		.schan_val = -10,
+		.schan_val2 = 123456,
+		.expected = "1240.710106203",
+	},
+	{
+		.name = "negative IIO_VAL_INT_PLUS_NANO, 3 negative",
+		.numerator = -1000000,
+		.denominator = -8060,
+		.schan_scale_type = IIO_VAL_INT_PLUS_NANO,
+		.schan_val = -10,
+		.schan_val2 = 123456,
+		.expected = "-1240.710106203",
+	},
+	{
+		.name = "negative IIO_VAL_INT_PLUS_NANO, 4 negative",
+		.numerator = -1000000,
+		.denominator = -8060,
+		.schan_scale_type = IIO_VAL_INT_PLUS_NANO,
+		.schan_val = -10,
+		.schan_val2 = -123456,
+		.expected = "-1240.710106203",
+	},
+	{
+		.name = "negative IIO_VAL_INT_PLUS_NANO, negative, *val = 0",
+		.numerator = 1,
+		.denominator = -10,
+		.schan_scale_type = IIO_VAL_INT_PLUS_NANO,
+		.schan_val = 0,
+		.schan_val2 = 123456789,
+		.expected = "-0.012345678",
+	},
+	/*
+	 * INT_PLUS_{MICRO,NANO} decimal part overflow
+	 */
+	{
+		.name = "decimal overflow IIO_VAL_INT_PLUS_NANO, positive",
+		.numerator = 1000000,
+		.denominator = 8060,
+		.schan_scale_type = IIO_VAL_INT_PLUS_NANO,
+		.schan_val = 10,
+		.schan_val2 = 123456789,
+		.expected = "1256.01200856",
+	},
+	{
+		.name = "decimal overflow IIO_VAL_INT_PLUS_NANO, negative",
+		.numerator = -1000000,
+		.denominator = 8060,
+		.schan_scale_type = IIO_VAL_INT_PLUS_NANO,
+		.schan_val = 10,
+		.schan_val2 = 123456789,
+		.expected = "-1256.01200856",
+	},
+	{
+		.name = "decimal overflow IIO_VAL_INT_PLUS_NANO, negative schan",
+		.numerator = 1000000,
+		.denominator = 8060,
+		.schan_scale_type = IIO_VAL_INT_PLUS_NANO,
+		.schan_val = -10,
+		.schan_val2 = 123456789,
+		.expected = "-1256.01200856",
+	},
+	{
+		.name = "decimal overflow IIO_VAL_INT_PLUS_MICRO, positive",
+		.numerator = 1000000,
+		.denominator = 8060,
+		.schan_scale_type = IIO_VAL_INT_PLUS_MICRO,
+		.schan_val = 10,
+		.schan_val2 = 123456789,
+		.expected = "16557.914267",
+	},
+	{
+		.name = "decimal overflow IIO_VAL_INT_PLUS_MICRO, negative",
+		.numerator = -1000000,
+		.denominator = 8060,
+		.schan_scale_type = IIO_VAL_INT_PLUS_MICRO,
+		.schan_val = 10,
+		.schan_val2 = 123456789,
+		.expected = "-16557.914267",
+	},
+	{
+		.name = "decimal overflow IIO_VAL_INT_PLUS_MICRO, negative schan",
+		.numerator = 1000000,
+		.denominator = 8060,
+		.schan_scale_type = IIO_VAL_INT_PLUS_MICRO,
+		.schan_val = -10,
+		.schan_val2 = 123456789,
+		.expected = "-16557.914267",
+	},
+	/*
+	 * 32-bit overflow conditions
+	 */
+	{
+		.name = "overflow IIO_VAL_FRACTIONAL, positive",
+		.numerator = 2,
+		.denominator = 20,
+		.schan_scale_type = IIO_VAL_FRACTIONAL,
+		.schan_val = S32_MAX,
+		.schan_val2 = 1,
+		.expected = "214748364.7",
+	},
+	{
+		.name = "overflow IIO_VAL_FRACTIONAL, negative",
+		.numerator = -2,
+		.denominator = 20,
+		.schan_scale_type = IIO_VAL_FRACTIONAL,
+		.schan_val = S32_MAX,
+		.schan_val2 = 1,
+		.expected = "-214748364.7",
+	},
+	{
+		.name = "overflow IIO_VAL_FRACTIONAL_LOG2, positive",
+		.numerator = S32_MAX,
+		.denominator = 4096,
+		.schan_scale_type = IIO_VAL_FRACTIONAL_LOG2,
+		.schan_val = 4096,
+		.schan_val2 = 16,
+		.expected = "32767.99998474121",
+	},
+	{
+		.name = "overflow IIO_VAL_FRACTIONAL_LOG2, negative",
+		.numerator = S32_MAX,
+		.denominator = 4096,
+		.schan_scale_type = IIO_VAL_FRACTIONAL_LOG2,
+		.schan_val = -4096,
+		.schan_val2 = 16,
+		.expected = "-32767.99998474121",
+	},
+	{
+		.name = "overflow IIO_VAL_INT_PLUS_NANO, positive",
+		.numerator = 2,
+		.denominator = 20,
+		.schan_scale_type = IIO_VAL_INT_PLUS_NANO,
+		.schan_val = 10,
+		.schan_val2 = S32_MAX,
+		.expected = "1.214748364",
+	},
+	{
+		.name = "overflow IIO_VAL_INT_PLUS_NANO, negative",
+		.numerator = -2,
+		.denominator = 20,
+		.schan_scale_type = IIO_VAL_INT_PLUS_NANO,
+		.schan_val = 10,
+		.schan_val2 = S32_MAX,
+		.expected = "-1.214748364",
+	},
+	{
+		.name = "overflow IIO_VAL_INT_PLUS_NANO, negative schan",
+		.numerator = 2,
+		.denominator = 20,
+		.schan_scale_type = IIO_VAL_INT_PLUS_NANO,
+		.schan_val = -10,
+		.schan_val2 = S32_MAX,
+		.expected = "-1.214748364",
+	},
+	{
+		.name = "overflow IIO_VAL_INT_PLUS_MICRO, positive",
+		.numerator = 2,
+		.denominator = 20,
+		.schan_scale_type = IIO_VAL_INT_PLUS_MICRO,
+		.schan_val = 10,
+		.schan_val2 = S32_MAX,
+		.expected = "215.748364",
+	},
+	{
+		.name = "overflow IIO_VAL_INT_PLUS_MICRO, negative",
+		.numerator = -2,
+		.denominator = 20,
+		.schan_scale_type = IIO_VAL_INT_PLUS_MICRO,
+		.schan_val = 10,
+		.schan_val2 = S32_MAX,
+		.expected = "-215.748364",
+	},
+	{
+		.name = "overflow IIO_VAL_INT_PLUS_MICRO, negative schan",
+		.numerator = 2,
+		.denominator = 20,
+		.schan_scale_type = IIO_VAL_INT_PLUS_MICRO,
+		.schan_val = -10,
+		.schan_val2 = S32_MAX,
+		.expected = "-215.748364",
+	},
+};
+
+const struct rescale_tc_data offset_cases[] = {
+	/*
+	 * Typical use cases
+	 */
+	{
+		.name = "typical IIO_VAL_INT, positive",
+		.offset = 1234,
+		.schan_scale_type = IIO_VAL_INT,
+		.schan_val = 123,
+		.schan_val2 = 0,
+		.schan_off = 14,
+		.expected_off = "24", /* 23.872 */
+	},
+	{
+		.name = "typical IIO_VAL_INT, negative",
+		.offset = -1234,
+		.schan_scale_type = IIO_VAL_INT,
+		.schan_val = 12,
+		.schan_val2 = 0,
+		.schan_off = 14,
+		.expected_off = "-88", /* -88.83333333333333 */
+	},
+	{
+		.name = "typical IIO_VAL_FRACTIONAL, positive",
+		.offset = 1234,
+		.schan_scale_type = IIO_VAL_FRACTIONAL,
+		.schan_val = 12,
+		.schan_val2 = 34,
+		.schan_off = 14,
+		.expected_off = "3510", /* 3510.333333333333 */
+	},
+	{
+		.name = "typical IIO_VAL_FRACTIONAL, negative",
+		.offset = -1234,
+		.schan_scale_type = IIO_VAL_FRACTIONAL,
+		.schan_val = 12,
+		.schan_val2 = 34,
+		.schan_off = 14,
+		.expected_off = "-3482", /* -3482.333333333333 */
+	},
+	{
+		.name = "typical IIO_VAL_FRACTIONAL_LOG2, positive",
+		.offset = 1234,
+		.schan_scale_type = IIO_VAL_FRACTIONAL_LOG2,
+		.schan_val = 12,
+		.schan_val2 = 16,
+		.schan_off = 14,
+		.expected_off = "6739299", /* 6739299.333333333 */
+	},
+	{
+		.name = "typical IIO_VAL_FRACTIONAL_LOG2, negative",
+		.offset = -1234,
+		.schan_scale_type = IIO_VAL_FRACTIONAL_LOG2,
+		.schan_val = 12,
+		.schan_val2 = 16,
+		.schan_off = 14,
+		.expected_off = "-6739271", /* -6739271.333333333 */
+	},
+	{
+		.name = "typical IIO_VAL_INT_PLUS_NANO, positive",
+		.offset = 1234,
+		.schan_scale_type = IIO_VAL_INT_PLUS_NANO,
+		.schan_val = 10,
+		.schan_val2 = 123456789,
+		.schan_off = 14,
+		.expected_off = "135", /* 135.8951219647469 */
+	},
+	{
+		.name = "typical IIO_VAL_INT_PLUS_NANO, negative",
+		.offset = -1234,
+		.schan_scale_type = IIO_VAL_INT_PLUS_NANO,
+		.schan_val = 10,
+		.schan_val2 = 123456789,
+		.schan_off = 14,
+		.expected_off = "-107", /* -107.89512196474689 */
+	},
+	{
+		.name = "typical IIO_VAL_INT_PLUS_MICRO, positive",
+		.offset = 1234,
+		.schan_scale_type = IIO_VAL_INT_PLUS_MICRO,
+		.schan_val = 10,
+		.schan_val2 = 123456789,
+		.schan_off = 14,
+		.expected_off = "23", /* 23.246438560723952 */
+	},
+	{
+		.name = "typical IIO_VAL_INT_PLUS_MICRO, negative",
+		.offset = -12345,
+		.schan_scale_type = IIO_VAL_INT_PLUS_MICRO,
+		.schan_val = 10,
+		.schan_val2 = 123456789,
+		.schan_off = 14,
+		.expected_off = "-78", /* -78.50185091745313 */
+	},
+};
+
+static void case_to_desc(const struct rescale_tc_data *t, char *desc)
+{
+	strcpy(desc, t->name);
+}
+
+KUNIT_ARRAY_PARAM(iio_rescale_scale, scale_cases, case_to_desc);
+KUNIT_ARRAY_PARAM(iio_rescale_offset, offset_cases, case_to_desc);
+
+/**
+ * iio_str_to_nano() - Parse a fixed-point string to get an
+ *                      IIO_VAL_INT_PLUS_NANO value
+ * @str: The string to parse
+ * @nano: The number as an integer
+ *
+ * Returns 0 on success, or a negative error code if the string cound not be
+ * parsed.
+ */
+static int iio_str_to_nano(const char *str, s64 *nano)
+{
+	int tmp, tmp2;
+	int ret = 0;
+
+	/*
+	 * iio_str_to_fixpoint() uses 10^8 here instead of 10^9 as fract_mult is
+	 * the multiplier for the first decimal place.
+	 */
+	ret = iio_str_to_fixpoint(str, 100000000, &tmp, &tmp2);
+	if (ret < 0)
+		return ret;
+
+	if (tmp < 0)
+		tmp2 *= -1;
+
+	*nano = (s64)tmp * GIGA + tmp2;
+
+	return ret;
+}
+
+/**
+ * iio_test_relative_error_ppm() - Compute relative error (in parts-per-million)
+ *                                 between two fixed-point strings
+ * @real_str: The real value as a string
+ * @exp_str: The expected value as a string
+ *
+ * Returns a negative error code if the strings cound not be parsed, or the
+ * relative error in parts-per-million.
+ */
+static int iio_test_relative_error_ppm(const char *real_str, const char *exp_str)
+{
+	s64 real, exp, err;
+	int ret;
+
+	ret = iio_str_to_nano(real_str, &real);
+	if (ret < 0)
+		return ret;
+
+	ret = iio_str_to_nano(exp_str, &exp);
+	if (ret < 0)
+		return ret;
+
+	if (!exp) {
+		pr_err("Expected value is null, relative error is undefined\n");
+		return -EINVAL;
+	}
+
+	err = MEGA * abs(exp - real);
+
+	return (int)div64_u64(err, abs(exp));
+}
+
+static void iio_rescale_test_scale(struct kunit *test)
+{
+	struct rescale_tc_data *t = (struct rescale_tc_data *)test->param_value;
+	char *buff = kunit_kmalloc(test, PAGE_SIZE, GFP_KERNEL);
+	struct rescale rescale;
+	int values[2];
+	int rel_ppm;
+	int ret;
+
+	rescale.numerator = t->numerator;
+	rescale.denominator = t->denominator;
+	rescale.offset = t->offset;
+	values[0] = t->schan_val;
+	values[1] = t->schan_val2;
+
+	ret = rescale_process_scale(&rescale, t->schan_scale_type,
+				    &values[0], &values[1]);
+
+	ret = iio_format_value(buff, ret, 2, values);
+	KUNIT_EXPECT_EQ(test, (int)strlen(buff), ret);
+
+	rel_ppm = iio_test_relative_error_ppm(buff, t->expected);
+	KUNIT_EXPECT_GE_MSG(test, rel_ppm, 0, "failed to compute ppm\n");
+
+	KUNIT_EXPECT_EQ_MSG(test, rel_ppm, 0,
+			    "\t    real=%s"
+			    "\texpected=%s\n",
+			    buff, t->expected);
+}
+
+static void iio_rescale_test_offset(struct kunit *test)
+{
+	struct rescale_tc_data *t = (struct rescale_tc_data *)test->param_value;
+	char *buff_off = kunit_kmalloc(test, PAGE_SIZE, GFP_KERNEL);
+	struct rescale rescale;
+	int values[2];
+	int ret;
+
+	rescale.numerator = t->numerator;
+	rescale.denominator = t->denominator;
+	rescale.offset = t->offset;
+	values[0] = t->schan_val;
+	values[1] = t->schan_val2;
+
+	ret = rescale_process_offset(&rescale, t->schan_scale_type,
+				     t->schan_val, t->schan_val2, t->schan_off,
+				     &values[0], &values[1]);
+
+	ret = iio_format_value(buff_off, ret, 2, values);
+	KUNIT_EXPECT_EQ(test, (int)strlen(buff_off), ret);
+
+	KUNIT_EXPECT_STREQ(test, strim(buff_off), t->expected_off);
+}
+
+static struct kunit_case iio_rescale_test_cases[] = {
+	KUNIT_CASE_PARAM(iio_rescale_test_scale, iio_rescale_scale_gen_params),
+	KUNIT_CASE_PARAM(iio_rescale_test_offset, iio_rescale_offset_gen_params),
+	{}
+};
+
+static struct kunit_suite iio_rescale_test_suite = {
+	.name = "iio-rescale",
+	.test_cases = iio_rescale_test_cases,
+};
+kunit_test_suite(iio_rescale_test_suite);
-- 
2.35.1.4.g5d01301f2b86

[PATCH v14 08/11] iio: afe: rescale: add RTD temperature sensor support

[Liam Beguin]

An RTD (Resistance Temperature Detector) is a kind of temperature
sensor used to get a linear voltage to temperature reading within a
give range (usually 0 to 100 degrees Celsius). Common types of RTDs
include PT100, PT500, and PT1000.

Signed-off-by: Liam Beguin <liambeguin@gmail.com>
Reviewed-by: Peter Rosin <peda@axentia.se>
---
 drivers/iio/afe/iio-rescale.c | 48 +++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
index 4601f84a83c2..beadf9fc0ee0 100644
--- a/drivers/iio/afe/iio-rescale.c
+++ b/drivers/iio/afe/iio-rescale.c
@@ -400,10 +400,52 @@ static int rescale_voltage_divider_props(struct device *dev,
 	return 0;
 }
 
+static int rescale_temp_sense_rtd_props(struct device *dev,
+					struct rescale *rescale)
+{
+	u32 factor;
+	u32 alpha;
+	u32 iexc;
+	u32 tmp;
+	int ret;
+	u32 r0;
+
+	ret = device_property_read_u32(dev, "excitation-current-microamp",
+				       &iexc);
+	if (ret) {
+		dev_err(dev, "failed to read excitation-current-microamp: %d\n",
+			ret);
+		return ret;
+	}
+
+	ret = device_property_read_u32(dev, "alpha-ppm-per-celsius", &alpha);
+	if (ret) {
+		dev_err(dev, "failed to read alpha-ppm-per-celsius: %d\n",
+			ret);
+		return ret;
+	}
+
+	ret = device_property_read_u32(dev, "r-naught-ohms", &r0);
+	if (ret) {
+		dev_err(dev, "failed to read r-naught-ohms: %d\n", ret);
+		return ret;
+	}
+
+	tmp = r0 * iexc * alpha / MEGA;
+	factor = gcd(tmp, MEGA);
+	rescale->numerator = MEGA / factor;
+	rescale->denominator = tmp / factor;
+
+	rescale->offset = -1 * ((r0 * iexc) / KILO);
+
+	return 0;
+}
+
 enum rescale_variant {
 	CURRENT_SENSE_AMPLIFIER,
 	CURRENT_SENSE_SHUNT,
 	VOLTAGE_DIVIDER,
+	TEMP_SENSE_RTD,
 };
 
 static const struct rescale_cfg rescale_cfg[] = {
@@ -419,6 +461,10 @@ static const struct rescale_cfg rescale_cfg[] = {
 		.type = IIO_VOLTAGE,
 		.props = rescale_voltage_divider_props,
 	},
+	[TEMP_SENSE_RTD] = {
+		.type = IIO_TEMP,
+		.props = rescale_temp_sense_rtd_props,
+	},
 };
 
 static const struct of_device_id rescale_match[] = {
@@ -428,6 +474,8 @@ static const struct of_device_id rescale_match[] = {
 	  .data = &rescale_cfg[CURRENT_SENSE_SHUNT], },
 	{ .compatible = "voltage-divider",
 	  .data = &rescale_cfg[VOLTAGE_DIVIDER], },
+	{ .compatible = "temperature-sense-rtd",
+	  .data = &rescale_cfg[TEMP_SENSE_RTD], },
 	{ /* sentinel */ }
 };
 MODULE_DEVICE_TABLE(of, rescale_match);
-- 
2.35.1.4.g5d01301f2b86

[PATCH v14 09/11] iio: afe: rescale: add temperature transducers

[Liam Beguin]

A temperature transducer is a device that converts a thermal quantity
into any other physical quantity. This patch adds support for
temperature to voltage (like the LTC2997) and temperature to current
(like the AD590) linear transducers.
In both cases these are assumed to be connected to a voltage ADC.

Signed-off-by: Liam Beguin <liambeguin@gmail.com>
Reviewed-by: Peter Rosin <peda@axentia.se>
---
 drivers/iio/afe/iio-rescale.c | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
index beadf9fc0ee0..45297530b878 100644
--- a/drivers/iio/afe/iio-rescale.c
+++ b/drivers/iio/afe/iio-rescale.c
@@ -441,11 +441,37 @@ static int rescale_temp_sense_rtd_props(struct device *dev,
 	return 0;
 }
 
+static int rescale_temp_transducer_props(struct device *dev,
+					 struct rescale *rescale)
+{
+	s32 offset = 0;
+	s32 sense = 1;
+	s32 alpha;
+	int ret;
+
+	device_property_read_u32(dev, "sense-offset-millicelsius", &offset);
+	device_property_read_u32(dev, "sense-resistor-ohms", &sense);
+	ret = device_property_read_u32(dev, "alpha-ppm-per-celsius", &alpha);
+	if (ret) {
+		dev_err(dev, "failed to read alpha-ppm-per-celsius: %d\n", ret);
+		return ret;
+	}
+
+	rescale->numerator = MEGA;
+	rescale->denominator = alpha * sense;
+
+	rescale->offset = div_s64((s64)offset * rescale->denominator,
+				  rescale->numerator);
+
+	return 0;
+}
+
 enum rescale_variant {
 	CURRENT_SENSE_AMPLIFIER,
 	CURRENT_SENSE_SHUNT,
 	VOLTAGE_DIVIDER,
 	TEMP_SENSE_RTD,
+	TEMP_TRANSDUCER,
 };
 
 static const struct rescale_cfg rescale_cfg[] = {
@@ -465,6 +491,10 @@ static const struct rescale_cfg rescale_cfg[] = {
 		.type = IIO_TEMP,
 		.props = rescale_temp_sense_rtd_props,
 	},
+	[TEMP_TRANSDUCER] = {
+		.type = IIO_TEMP,
+		.props = rescale_temp_transducer_props,
+	},
 };
 
 static const struct of_device_id rescale_match[] = {
@@ -476,6 +506,8 @@ static const struct of_device_id rescale_match[] = {
 	  .data = &rescale_cfg[VOLTAGE_DIVIDER], },
 	{ .compatible = "temperature-sense-rtd",
 	  .data = &rescale_cfg[TEMP_SENSE_RTD], },
+	{ .compatible = "temperature-transducer",
+	  .data = &rescale_cfg[TEMP_TRANSDUCER], },
 	{ /* sentinel */ }
 };
 MODULE_DEVICE_TABLE(of, rescale_match);
-- 
2.35.1.4.g5d01301f2b86

[PATCH v14 10/11] dt-bindings: iio: afe: add bindings for temperature-sense-rtd

[Liam Beguin]

An ADC is often used to measure other quantities indirectly. This
binding describe one case, the measurement of a temperature through the
voltage across an RTD resistor such as a PT1000.

Signed-off-by: Liam Beguin <liambeguin@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Peter Rosin <peda@axentia.se>
---
 .../iio/afe/temperature-sense-rtd.yaml        | 101 ++++++++++++++++++
 1 file changed, 101 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml

diff --git a/Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml b/Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml
new file mode 100644
index 000000000000..336ce96371db
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml
@@ -0,0 +1,101 @@
+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/afe/temperature-sense-rtd.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Temperature Sense RTD
+
+maintainers:
+  - Liam Beguin <liambeguin@gmail.com>
+
+description: |
+  RTDs (Resistance Temperature Detectors) are a kind of temperature sensors
+  used to get a linear voltage to temperature reading within a give range
+  (usually 0 to 100 degrees Celsius).
+
+  When an io-channel measures the output voltage across an RTD such as a
+  PT1000, the interesting measurement is almost always the corresponding
+  temperature, not the voltage output. This binding describes such a circuit.
+
+  The general transfer function here is (using SI units)
+
+    V = R(T) * iexc
+    R(T) = r0 * (1 + alpha * T)
+    T = 1 / (alpha * r0 * iexc) * (V - r0 * iexc)
+
+  The following circuit matches what's in the examples section.
+
+           5V0
+          -----
+            |
+        +---+----+
+        |  R 5k  |
+        +---+----+
+            |
+            V 1mA
+            |
+            +---- Vout
+            |
+        +---+----+
+        | PT1000 |
+        +---+----+
+            |
+          -----
+           GND
+
+properties:
+  compatible:
+    const: temperature-sense-rtd
+
+  io-channels:
+    maxItems: 1
+    description: |
+      Channel node of a voltage io-channel.
+
+  '#io-channel-cells':
+    const: 0
+
+  excitation-current-microamp:
+    description: The current fed through the RTD sensor.
+
+  alpha-ppm-per-celsius:
+    description: |
+      alpha can also be expressed in micro-ohms per ohm Celsius. It's a linear
+      approximation of the resistance versus temperature relationship
+      between 0 and 100 degrees Celsius.
+
+      alpha = (R_100 - R_0) / (100 * R_0)
+
+      Where, R_100 is the resistance of the sensor at 100 degrees Celsius, and
+      R_0 (or r-naught-ohms) is the resistance of the sensor at 0 degrees
+      Celsius.
+
+      Pure platinum has an alpha of 3925. Industry standards such as IEC60751
+      and ASTM E-1137 specify an alpha of 3850.
+
+  r-naught-ohms:
+    description: |
+      Resistance of the sensor at 0 degrees Celsius.
+      Common values are 100 for PT100, 500 for PT500, and 1000 for PT1000
+
+additionalProperties: false
+required:
+  - compatible
+  - io-channels
+  - excitation-current-microamp
+  - alpha-ppm-per-celsius
+  - r-naught-ohms
+
+examples:
+  - |
+    pt1000_1: temperature-sensor0 {
+        compatible = "temperature-sense-rtd";
+        #io-channel-cells = <0>;
+        io-channels = <&temp_adc1 0>;
+
+        excitation-current-microamp = <1000>; /* i = U/R = 5 / 5000 */
+        alpha-ppm-per-celsius = <3908>;
+        r-naught-ohms = <1000>;
+    };
+...
-- 
2.35.1.4.g5d01301f2b86

[PATCH v14 11/11] dt-bindings: iio: afe: add bindings for temperature transducers

[Liam Beguin]

An ADC is often used to measure other quantities indirectly.
This binding describe one case, the measurement of a temperature
through a temperature transducer (either voltage or current).

Signed-off-by: Liam Beguin <liambeguin@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Peter Rosin <peda@axentia.se>
---
 .../iio/afe/temperature-transducer.yaml       | 114 ++++++++++++++++++
 1 file changed, 114 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml

diff --git a/Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml b/Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml
new file mode 100644
index 000000000000..cfbf5350db27
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml
@@ -0,0 +1,114 @@
+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/afe/temperature-transducer.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Temperature Transducer
+
+maintainers:
+  - Liam Beguin <liambeguin@gmail.com>
+
+description: |
+  A temperature transducer is a device that converts a thermal quantity
+  into any other physical quantity. This binding applies to temperature to
+  voltage (like the LTC2997), and temperature to current (like the AD590)
+  linear transducers.
+  In both cases these are assumed to be connected to a voltage ADC.
+
+  When an io-channel measures the output voltage of a temperature analog front
+  end such as a temperature transducer, the interesting measurement is almost
+  always the corresponding temperature, not the voltage output. This binding
+  describes such a circuit.
+
+  The general transfer function here is (using SI units)
+    V(T) = Rsense * Isense(T)
+    T = (Isense(T) / alpha) + offset
+    T = 1 / (Rsense * alpha) * (V + offset * Rsense * alpha)
+
+  When using a temperature to voltage transducer, Rsense is set to 1.
+
+  The following circuits show a temperature to current and a temperature to
+  voltage transducer that can be used with this binding.
+
+           VCC
+          -----
+            |
+        +---+---+
+        | AD590 |                               VCC
+        +---+---+                              -----
+            |                                    |
+            V proportional to T             +----+----+
+            |                          D+ --+         |
+            +---- Vout                      | LTC2997 +--- Vout
+            |                          D- --+         |
+        +---+----+                          +---------+
+        | Rsense |                               |
+        +---+----+                             -----
+            |                                   GND
+          -----
+           GND
+
+properties:
+  compatible:
+    const: temperature-transducer
+
+  io-channels:
+    maxItems: 1
+    description: |
+      Channel node of a voltage io-channel.
+
+  '#io-channel-cells':
+    const: 0
+
+  sense-offset-millicelsius:
+    description: |
+      Temperature offset.
+      This offset is commonly used to convert from Kelvins to degrees Celsius.
+      In that case, sense-offset-millicelsius would be set to <(-273150)>.
+    default: 0
+
+  sense-resistor-ohms:
+    description: |
+      The sense resistor.
+      By default sense-resistor-ohms cancels out the resistor making the
+      circuit behave like a temperature transducer.
+    default: 1
+
+  alpha-ppm-per-celsius:
+    description: |
+      Sometimes referred to as output gain, slope, or temperature coefficient.
+
+      alpha is expressed in parts per million which can be micro-amps per
+      degrees Celsius or micro-volts per degrees Celsius. The is the main
+      characteristic of a temperature transducer and should be stated in the
+      datasheet.
+
+additionalProperties: false
+
+required:
+  - compatible
+  - io-channels
+  - alpha-ppm-per-celsius
+
+examples:
+  - |
+    ad950: temperature-sensor-0 {
+        compatible = "temperature-transducer";
+        #io-channel-cells = <0>;
+        io-channels = <&temp_adc 3>;
+
+        sense-offset-millicelsius = <(-273150)>; /* Kelvin to degrees Celsius */
+        sense-resistor-ohms = <8060>;
+        alpha-ppm-per-celsius = <1>; /* 1 uA/K */
+    };
+  - |
+    znq_tmp: temperature-sensor-1 {
+        compatible = "temperature-transducer";
+        #io-channel-cells = <0>;
+        io-channels = <&temp_adc 2>;
+
+        sense-offset-millicelsius = <(-273150)>; /* Kelvin to degrees Celsius */
+        alpha-ppm-per-celsius = <4000>; /* 4 mV/K */
+    };
+...
-- 
2.35.1.4.g5d01301f2b86

Re: [PATCH v14 03/11] iio: afe: rescale: add offset support

[Andy Shevchenko]

On Tue, Feb 8, 2022 at 4:04 AM Liam Beguin <liambeguin@gmail.com> wrote:
>
> This is a preparatory change required for the addition of temperature
> sensing front ends.

...

> +               if (iio_channel_has_info(rescale->source->channel,
> +                                        IIO_CHAN_INFO_OFFSET)) {
> +                       ret = iio_read_channel_offset(rescale->source,
> +                                                     &schan_off, NULL);

> +                       if (ret != IIO_VAL_INT)
> +                               return ret < 0 ? ret : -EOPNOTSUPP;

Wonder if this actually should be

   if (ret < 0)
       return ret;
   if (ret != ...)
       return -EOP...;

> +               }

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v14 09/11] iio: afe: rescale: add temperature transducers

[Andy Shevchenko]

On Tue, Feb 8, 2022 at 4:04 AM Liam Beguin <liambeguin@gmail.com> wrote:
>
> A temperature transducer is a device that converts a thermal quantity
> into any other physical quantity. This patch adds support for
> temperature to voltage (like the LTC2997) and temperature to current
> (like the AD590) linear transducers.
> In both cases these are assumed to be connected to a voltage ADC.

...

> +       rescale->offset = div_s64((s64)offset * rescale->denominator,
> +                                 rescale->numerator);

Wonder if we can use mult_frac() here. Would it require 64-bit division?

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v14 03/11] iio: afe: rescale: add offset support

[Liam Beguin]

Hi Andy,

On Tue, Feb 08, 2022 at 03:42:22PM +0200, Andy Shevchenko wrote:
> On Tue, Feb 8, 2022 at 4:04 AM Liam Beguin <liambeguin@gmail.com> wrote:
> >
> > This is a preparatory change required for the addition of temperature
> > sensing front ends.
> 
> ...
> 
> > +               if (iio_channel_has_info(rescale->source->channel,
> > +                                        IIO_CHAN_INFO_OFFSET)) {
> > +                       ret = iio_read_channel_offset(rescale->source,
> > +                                                     &schan_off, NULL);
> 
> > +                       if (ret != IIO_VAL_INT)
> > +                               return ret < 0 ? ret : -EOPNOTSUPP;
> 
> Wonder if this actually should be
> 
>    if (ret < 0)
>        return ret;
>    if (ret != ...)
>        return -EOP...;

Unless someone has a stong objection, I'd rather keep it as is.

Cheers,
Liam

> > +               }
> 
> -- 
> With Best Regards,
> Andy Shevchenko

Re: [PATCH v14 09/11] iio: afe: rescale: add temperature transducers

[Liam Beguin]

Hi Andy,

On Tue, Feb 08, 2022 at 03:46:27PM +0200, Andy Shevchenko wrote:
> On Tue, Feb 8, 2022 at 4:04 AM Liam Beguin <liambeguin@gmail.com> wrote:
> >
> > A temperature transducer is a device that converts a thermal quantity
> > into any other physical quantity. This patch adds support for
> > temperature to voltage (like the LTC2997) and temperature to current
> > (like the AD590) linear transducers.
> > In both cases these are assumed to be connected to a voltage ADC.
> 
> ...
> 
> > +       rescale->offset = div_s64((s64)offset * rescale->denominator,
> > +                                 rescale->numerator);
> 
> Wonder if we can use mult_frac() here. Would it require 64-bit division?

Same here, I'd rather keep it as is, especially if you plan on adding
helpers later on for struct u32_fract.

Cheers,
Liam

> -- 
> With Best Regards,
> Andy Shevchenko

Re: [PATCH v14 02/11] iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support

[Peter Rosin]

Hi!

As usual, sorry for my low bandwidth.

On 2022-02-08 03:04, Liam Beguin wrote:
> Some ADCs use IIO_VAL_INT_PLUS_{NANO,MICRO} scale types.
> Add support for these to allow using the iio-rescaler with them.
> 
> Signed-off-by: Liam Beguin <liambeguin@gmail.com>
> Reviewed-by: Peter Rosin <peda@axentia.se>
> ---
>  drivers/iio/afe/iio-rescale.c | 35 +++++++++++++++++++++++++++++++++++
>  1 file changed, 35 insertions(+)
> 
> diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
> index 65832dd09249..f833eb38f8bb 100644
> --- a/drivers/iio/afe/iio-rescale.c
> +++ b/drivers/iio/afe/iio-rescale.c
> @@ -14,6 +14,7 @@
>  #include <linux/of_device.h>
>  #include <linux/platform_device.h>
>  #include <linux/property.h>
> +#include <linux/units.h>
>  
>  #include <linux/iio/afe/rescale.h>
>  #include <linux/iio/consumer.h>
> @@ -23,6 +24,9 @@ int rescale_process_scale(struct rescale *rescale, int scale_type,
>  			  int *val, int *val2)
>  {
>  	s64 tmp;
> +	s32 rem;
> +	u32 mult;
> +	u32 neg;
>  
>  	switch (scale_type) {
>  	case IIO_VAL_FRACTIONAL:
> @@ -41,6 +45,37 @@ int rescale_process_scale(struct rescale *rescale, int scale_type,
>  		tmp *= rescale->numerator;
>  		tmp = div_s64(tmp, 1000000000LL);
>  		*val = tmp;
> +		return scale_type;
> +	case IIO_VAL_INT_PLUS_NANO:
> +	case IIO_VAL_INT_PLUS_MICRO:
> +		mult = scale_type == IIO_VAL_INT_PLUS_NANO ? GIGA : MEGA;

By now, we all agree that the big numbers in this context have nothing
to do with unit prefixes of physical quantities, so the macros are not
really appropriate. However, in this case we have IIO_VAL_INT_PLUS_NANO
and IIO_VAL_INT_PLUS_MICRO. Not using "NANO : MICRO" here, and instead
go with "GIGA : MEGA" is just plain silly, if you ask me.

So, either "NANO : MICRO" or "1000000000 : 1000000".

I'm not sold on the macros. I frankly don't see all that much value
in them and am perfectly fine with raw numbers. To me, it just looks
like someone has read somewhere that constants should not appear in
the code, and from that concluded that #define TEN 10 is a good thing
without thinking very much about it. There is also the possibility
that someone who has never seen these defines thinks MEGA is 2^20
instead of 10^6, because that is a much more likely candidate for a
define in the frist place (not everybody knows all the digits of
1048576 by heart and 1 << 20 many times require extra brackets that
might make it look more complicated than it needs to be).

Back to this case; the connection to the naming of IIO_VAL_INT_PLUS_NANO
(and ..._MICRO) makes it ok to use the defines. So if you feel strongly
about not using "1000000000 : 1000000" I'm ok with that.

Cheers,
Peter

> +
> +		/*
> +		 * For IIO_VAL_INT_PLUS_{MICRO,NANO} scale types if either *val
> +		 * OR *val2 is negative the schan scale is negative, i.e.
> +		 * *val = 1 and *val2 = -0.5 yields -1.5 not -0.5.
> +		 */
> +		neg = *val < 0 || *val2 < 0;
> +
> +		tmp = (s64)abs(*val) * abs(rescale->numerator);
> +		*val = div_s64_rem(tmp, abs(rescale->denominator), &rem);
> +
> +		tmp = (s64)rem * mult + (s64)abs(*val2) * abs(rescale->numerator);
> +		tmp = div_s64(tmp, abs(rescale->denominator));
> +
> +		*val += div_s64_rem(tmp, mult, val2);
> +
> +		/*
> +		 * If only one of the rescaler elements or the schan scale is
> +		 * negative, the combined scale is negative.
> +		 */
> +		if (neg ^ ((rescale->numerator < 0) ^ (rescale->denominator < 0))) {
> +			if (*val)
> +				*val = -*val;
> +			else
> +				*val2 = -*val2;
> +		}
> +
>  		return scale_type;
>  	default:
>  		return -EOPNOTSUPP;

Re: [PATCH v14 03/11] iio: afe: rescale: add offset support

[Peter Rosin]

Hi!

On 2022-02-08 03:04, Liam Beguin wrote:
> This is a preparatory change required for the addition of temperature
> sensing front ends.
> 
> Signed-off-by: Liam Beguin <liambeguin@gmail.com>
> Reviewed-by: Peter Rosin <peda@axentia.se>
> ---
>  drivers/iio/afe/iio-rescale.c   | 81 +++++++++++++++++++++++++++++++++
>  include/linux/iio/afe/rescale.h |  4 ++
>  2 files changed, 85 insertions(+)
> 
> diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
> index f833eb38f8bb..63035b4bce5e 100644
> --- a/drivers/iio/afe/iio-rescale.c
> +++ b/drivers/iio/afe/iio-rescale.c
> @@ -3,6 +3,7 @@
>   * IIO rescale driver
>   *
>   * Copyright (C) 2018 Axentia Technologies AB
> + * Copyright (C) 2022 Liam Beguin <liambeguin@gmail.com>
>   *
>   * Author: Peter Rosin <peda@axentia.se>
>   */
> @@ -82,11 +83,46 @@ int rescale_process_scale(struct rescale *rescale, int scale_type,
>  	}
>  }
>  
> +int rescale_process_offset(struct rescale *rescale, int scale_type,
> +			   int scale, int scale2, int schan_off,
> +			   int *val, int *val2)
> +{
> +	s64 tmp, tmp2;
> +
> +	switch (scale_type) {
> +	case IIO_VAL_FRACTIONAL:
> +		tmp = (s64)rescale->offset * scale2;
> +		*val = div_s64(tmp, scale) + schan_off;
> +		return IIO_VAL_INT;
> +	case IIO_VAL_INT:
> +		*val = div_s64(rescale->offset, scale) + schan_off;
> +		return IIO_VAL_INT;
> +	case IIO_VAL_FRACTIONAL_LOG2:
> +		tmp = (s64)rescale->offset * (1 << scale2);
> +		*val = div_s64(tmp, scale) + schan_off;
> +		return IIO_VAL_INT;
> +	case IIO_VAL_INT_PLUS_NANO:
> +		tmp = (s64)rescale->offset * GIGA;
> +		tmp2 = ((s64)scale * GIGA) + scale2;

Same thing here as in patch 2/11, use NANO or the raw number. GIGA
has no connection to the usage.

> +		*val = div64_s64(tmp, tmp2) + schan_off;
> +		return IIO_VAL_INT;
> +	case IIO_VAL_INT_PLUS_MICRO:
> +		tmp = (s64)rescale->offset * MEGA;
> +		tmp2 = ((s64)scale * MEGA) + scale2;

And MICRO here of course.

Cheers,
Peter

*snip*

Re: [PATCH v14 02/11] iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support

[Liam Beguin]

Hi Peter,

On Thu, Feb 10, 2022 at 05:42:25PM +0100, Peter Rosin wrote:
> Hi!
> 
> As usual, sorry for my low bandwidth.

No worries, I understand. It's been pretty slow on my end as well.

Thanks for still making time for this :-)

> On 2022-02-08 03:04, Liam Beguin wrote:
> > Some ADCs use IIO_VAL_INT_PLUS_{NANO,MICRO} scale types.
> > Add support for these to allow using the iio-rescaler with them.
> > 
> > Signed-off-by: Liam Beguin <liambeguin@gmail.com>
> > Reviewed-by: Peter Rosin <peda@axentia.se>
> > ---
> >  drivers/iio/afe/iio-rescale.c | 35 +++++++++++++++++++++++++++++++++++
> >  1 file changed, 35 insertions(+)

...

> > @@ -41,6 +45,37 @@ int rescale_process_scale(struct rescale *rescale, int scale_type,
> >  		tmp *= rescale->numerator;
> >  		tmp = div_s64(tmp, 1000000000LL);
> >  		*val = tmp;
> > +		return scale_type;
> > +	case IIO_VAL_INT_PLUS_NANO:
> > +	case IIO_VAL_INT_PLUS_MICRO:
> > +		mult = scale_type == IIO_VAL_INT_PLUS_NANO ? GIGA : MEGA;
> 
> By now, we all agree that the big numbers in this context have nothing
> to do with unit prefixes of physical quantities, so the macros are not
> really appropriate. However, in this case we have IIO_VAL_INT_PLUS_NANO
> and IIO_VAL_INT_PLUS_MICRO. Not using "NANO : MICRO" here, and instead
> go with "GIGA : MEGA" is just plain silly, if you ask me.
> 
> So, either "NANO : MICRO" or "1000000000 : 1000000".
> 
> I'm not sold on the macros. I frankly don't see all that much value
> in them and am perfectly fine with raw numbers. To me, it just looks
> like someone has read somewhere that constants should not appear in
> the code, and from that concluded that #define TEN 10 is a good thing
> without thinking very much about it. There is also the possibility
> that someone who has never seen these defines thinks MEGA is 2^20
> instead of 10^6, because that is a much more likely candidate for a
> define in the frist place (not everybody knows all the digits of
> 1048576 by heart and 1 << 20 many times require extra brackets that
> might make it look more complicated than it needs to be).
> 
> Back to this case; the connection to the naming of IIO_VAL_INT_PLUS_NANO
> (and ..._MICRO) makes it ok to use the defines. So if you feel strongly
> about not using "1000000000 : 1000000" I'm ok with that.

I like that the macros make the number of zeros more "obvious" in a
sense, but honestly at this point, I'd rather go back to not using them.
Depending on who you ask, one way makes more sense than the other, at
least with the raw values, there's no ambiguity.

Cheers,
Liam

> Cheers,
> Peter

Re: [PATCH v14 06/11] iio: afe: rescale: make use of units.h

[Peter Rosin]

Hi!

On 2022-02-08 03:04, Liam Beguin wrote:
> Make use of well-defined SI metric prefixes to improve code readability.
> 
> Signed-off-by: Liam Beguin <liambeguin@gmail.com>
> ---
>  drivers/iio/afe/iio-rescale.c | 19 ++++++++++++-------
>  1 file changed, 12 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/iio/afe/iio-rescale.c b/drivers/iio/afe/iio-rescale.c
> index 67273de46843..4601f84a83c2 100644
> --- a/drivers/iio/afe/iio-rescale.c
> +++ b/drivers/iio/afe/iio-rescale.c
> @@ -51,11 +51,16 @@ int rescale_process_scale(struct rescale *rescale, int scale_type,
>  		}
>  		fallthrough;
>  	case IIO_VAL_FRACTIONAL_LOG2:
> -		tmp = (s64)*val * 1000000000LL;
> +		/*
> +		 * GIGA is used here as an arbitrarily large multiplier to avoid

s/arbitrarily/arbitrary/, however...

> +		 * precision loss in the division. It doesn't have any physical
> +		 * meaning attached to it.

... 1000000000 is NOT arbitrary. Before patch 4/11 that was true, but
with that patch the multiplier MUST match the multiplier used below
when calculating with the decimals for the IIO_VAL_INT_PLUS_NANO
value. Again, the connection with that name makes me think that NANO
is just so much better that GIGA. Still fine with raw numbers of
course.

So, the comment is actively misleading. How about the following?

/*
 * We need to multiply by something large to avoid loss of
 * precision, and NANO fits that while at the same time
 * being compatible with the conversion to
 * IIO_VAL_INT_PLUS_NANO for cases where that maintains even
 * more precision.
 */

> +		 */
> +		tmp = (s64)*val * GIGA;
>  		tmp = div_s64(tmp, rescale->denominator);
>  		tmp *= rescale->numerator;
>  
> -		tmp = div_s64_rem(tmp, 1000000000LL, &rem);
> +		tmp = div_s64_rem(tmp, GIGA, &rem);
>  		*val = tmp;
>  
>  		if (!rem)
> @@ -71,7 +76,7 @@ int rescale_process_scale(struct rescale *rescale, int scale_type,
>  
>  		*val2 = rem / (int)tmp;
>  		if (rem2)
> -			*val2 += div_s64((s64)rem2 * 1000000000LL, tmp);
> +			*val2 += div_s64((s64)rem2 * GIGA, tmp);

NANO again, because IIO_VAL_INT_PLUS_NANO.

>  
>  		return IIO_VAL_INT_PLUS_NANO;
>  	case IIO_VAL_INT_PLUS_NANO:
> @@ -332,8 +337,8 @@ static int rescale_current_sense_amplifier_props(struct device *dev,
>  	 * gain_div / (gain_mult * sense), while trying to keep the
>  	 * numerator/denominator from overflowing.
>  	 */
> -	factor = gcd(sense, 1000000);
> -	rescale->numerator = 1000000 / factor;
> +	factor = gcd(sense, MEGA);
> +	rescale->numerator = MEGA / factor;

Here, we actually have a connection with prefix of a unit of a
physical quantity. microohms. If anything, why not MICRO?

>  	rescale->denominator = sense / factor;
>  
>  	factor = gcd(rescale->numerator, gain_mult);
> @@ -361,8 +366,8 @@ static int rescale_current_sense_shunt_props(struct device *dev,
>  		return ret;
>  	}
>  
> -	factor = gcd(shunt, 1000000);
> -	rescale->numerator = 1000000 / factor;
> +	factor = gcd(shunt, MEGA);
> +	rescale->numerator = MEGA / factor;

MICRO again, bacause microohms.

>  	rescale->denominator = shunt / factor;
>  
>  	return 0;

Cheers,
Peter

Re: [PATCH v14 02/11] iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support

[Peter Rosin]

On 2022-02-10 18:36, Liam Beguin wrote:
> I like that the macros make the number of zeros more "obvious" in a
> sense, but honestly at this point, I'd rather go back to not using them.
> Depending on who you ask, one way makes more sense than the other, at
> least with the raw values, there's no ambiguity.

I'm fine with not using the macros in this series, obviously. While I
can tolerate them, I do not get a warm and cozy feeling when I see
them.

Cheers,
Peter