[PATCH v3 00/10] iio: afe: add temperature rescaling support

From: Liam Beguin
Date: Wed Jun 30 2021 - 21:01:06 EST

From: Liam Beguin <lvb@xxxxxxxxxx>

Add temperature rescaling support to the IIO Analog Front End driver.

This series includes minor bug fixes and adds support for RTD temperature
sensors as well as temperature transducers.

At first I tried to use iio_convert_raw_to_processed() to get more
precision out of processed values but ran into issues when one of my
ADCs didn't provide a scale. I tried to address this in the first two
patches.

When adding offset support to iio-rescale, I also noticed that
iio_read_channel_processed() assumes that the offset is always an
integer which I tried to address in the third patch without breaking
valid implicit truncations.

Related to: https://patchwork.kernel.org/project/linux-iio/list/?series=483087

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

Thanks for your time

Liam Beguin (10):
iio: inkern: apply consumer scale on IIO_VAL_INT cases
iio: inkern: apply consumer scale when no channel scale is available
iio: inkern: make a best effort on offset calculation
iio: afe: rescale: reduce risk of integer overflow
iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support
iio: afe: rescale: add offset support
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 | 111 ++++++++++++
MAINTAINERS | 8 +
drivers/iio/afe/iio-rescale.c | 163 +++++++++++++++++-
drivers/iio/inkern.c | 44 ++++-
5 files changed, 415 insertions(+), 12 deletions(-)
create mode 100644 Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml
create mode 100644 Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml

Range-diff against v2:
1: eb81d6b5ed88 = 1: 42a7a1047edc iio: inkern: apply consumer scale on IIO_VAL_INT cases
2: d132d86c0dd2 = 2: a1cd89fdad11 iio: inkern: apply consumer scale when no channel scale is available
3: 7a659ccc5d7b ! 3: e74ff6b2f663 iio: inkern: error out on unsupported offset type
@@ Metadata
Author: Liam Beguin <liambeguin@xxxxxxxxx>

## Commit message ##
- iio: inkern: error out on unsupported offset type
+ iio: inkern: make a best effort on offset calculation

iio_convert_raw_to_processed_unlocked() assumes the offset is an
- integer.
- Make that clear to the consumer by returning an error on unsupported
- offset types without breaking valid implicit truncations.
+ integer. Make a best effort to get a valid offset value for fractional
+ cases without breaking implicit truncations.

+ Fixes: 48e44ce0f881 ("iio:inkern: Add function to read the processed value")
Signed-off-by: Liam Beguin <lvb@xxxxxxxxxx>

## drivers/iio/inkern.c ##
@@ drivers/iio/inkern.c: EXPORT_SYMBOL_GPL(iio_read_channel_average_raw);
+ int offset_type, offset_val, offset_val2;
s64 raw64 = raw;
- int ret;
++ int tmp;

- ret = iio_channel_read(chan, &offset, NULL, IIO_CHAN_INFO_OFFSET);
- if (ret >= 0)
@@ drivers/iio/inkern.c: EXPORT_SYMBOL_GPL(iio_read_channel_average_raw);
+ case IIO_VAL_INT:
+ break;
+ case IIO_VAL_INT_PLUS_MICRO:
-+ if (offset_val2 > 1000)
-+ return -EINVAL;
-+ break;
++ fallthrough;
+ case IIO_VAL_INT_PLUS_NANO:
-+ if (offset_val2 > 1000000)
-+ return -EINVAL;
++ /*
++ * Both IIO_VAL_INT_PLUS_MICRO and IIO_VAL_INT_PLUS_NANO
++ * implicitely truncate the offset to it's integer form.
++ */
++ break;
+ case IIO_VAL_FRACTIONAL:
-+ if (offset_val2 != 1)
-+ return -EINVAL;
++ tmp = offset_val / offset_val2;
++ offset_val = tmp;
+ break;
+ case IIO_VAL_FRACTIONAL_LOG2:
-+ if (offset_val2)
-+ return -EINVAL;
++ tmp = offset_val / (1 << offset_val2);
++ offset_val = tmp;
+ break;
+ default:
+ return -EINVAL;
4: 272d29f21eac < -: ------------ iio: inkern: return valid type on raw to processed conversion
5: ab38421fbae2 < -: ------------ iio: afe: rescale: add upstream offset support
-: ------------ > 4: a5696ca3c14f iio: afe: rescale: reduce risk of integer overflow
-: ------------ > 5: 2b435a2f58e8 iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support
6: 59e93788dd28 ! 6: 577020b8326b iio: afe: rescale: add offset support
@@ drivers/iio/afe/iio-rescale.c: struct rescale {

static int rescale_read_raw(struct iio_dev *indio_dev,
@@ drivers/iio/afe/iio-rescale.c: static int rescale_read_raw(struct iio_dev *indio_dev,
- default:
+ int *val, int *val2, long mask)
+ {
+ struct rescale *rescale = iio_priv(indio_dev);
++ int scale, scale2;
++ int schan_off = 0;
+ s64 tmp, tmp2;
+ u32 factor;
+ int ret;
+@@ drivers/iio/afe/iio-rescale.c: static int rescale_read_raw(struct iio_dev *indio_dev,
+ dev_err(&indio_dev->dev, "unsupported type %d\n", ret);
return -EOPNOTSUPP;
}
+ case IIO_CHAN_INFO_OFFSET:
-+ *val = rescale->offset;
++ /*
++ * Processed channels are scaled 1-to-1 and source offset is
++ * already taken into account.
++ *
++ * In other cases, the final offset value is defined by:
++ * 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 < 0)
++ return ret;
++ else if (ret != IIO_VAL_INT)
++ return -EOPNOTSUPP;
++ }
+
-+ return IIO_VAL_INT;
++ ret = iio_read_channel_scale(rescale->source, &scale, &scale2);
++ switch (ret) {
++ 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 * 1000000000UL;
++ tmp2 = ((s64)scale * 1000000000UL) + scale2;
++ factor = gcd(tmp, tmp2);
++ tmp /= factor;
++ tmp2 /= factor;
++ *val = div_s64(tmp, tmp2) + schan_off;
++ return IIO_VAL_INT;
++ case IIO_VAL_INT_PLUS_MICRO:
++ tmp = (s64)rescale->offset * 1000000UL;
++ tmp2 = ((s64)scale * 1000000UL) + scale2;
++ factor = gcd(tmp, tmp2);
++ tmp /= factor;
++ tmp2 /= factor;
++ *val = div_s64(tmp, tmp2) + schan_off;
++ return IIO_VAL_INT;
++ default:
++ dev_err(&indio_dev->dev, "unsupported type %d\n", ret);
++ return -EOPNOTSUPP;
++ }
default:
return -EINVAL;
}
7: b413cb4f190b < -: ------------ iio: afe: rescale: add temperature sensor support
8: 3f6564f5a346 < -: ------------ dt-bindings: iio: afe: add binding for temperature-sense-amplifier
-: ------------ > 7: 0add5863ff00 iio: afe: rescale: add RTD temperature sensor support
-: ------------ > 8: 0306e16020d4 iio: afe: rescale: add temperature transducers
-: ------------ > 9: 6906c5a21861 dt-bindings: iio: afe: add bindings for temperature-sense-rtd
-: ------------ > 10: ac8d4eef179b dt-bindings: iio: afe: add bindings for temperature transducers

base-commit: 6cbb3aa0f9d5d23221df787cf36f74d3866fdb78
--
2.30.1.489.g328c10930387