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Subject[PATCH v4 00/10] iio: afe: add temperature rescaling support
Date
From: Liam Beguin <lvb@xiphos.com>

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 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

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 +++++++++++
drivers/iio/afe/iio-rescale.c | 173 +++++++++++++++++-
drivers/iio/inkern.c | 40 +++-
4 files changed, 413 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 v3:
-: ------------ > 1: 42a7a1047edc iio: inkern: apply consumer scale on IIO_VAL_INT cases
-: ------------ > 2: a1cd89fdad11 iio: inkern: apply consumer scale when no channel scale is available
1: e74ff6b2f663 ! 3: ed0721fb6bd1 iio: inkern: make a best effort on offset calculation
@@ 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:
-+ fallthrough;
+ case IIO_VAL_INT_PLUS_NANO:
+ /*
+ * Both IIO_VAL_INT_PLUS_MICRO and IIO_VAL_INT_PLUS_NANO
@@ drivers/iio/inkern.c: EXPORT_SYMBOL_GPL(iio_read_channel_average_raw);
+ */
+ break;
+ case IIO_VAL_FRACTIONAL:
-+ tmp = offset_val / offset_val2;
-+ offset_val = tmp;
++ offset_val /= offset_val2;
+ break;
+ case IIO_VAL_FRACTIONAL_LOG2:
-+ tmp = offset_val / (1 << offset_val2);
-+ offset_val = tmp;
++ offset_val /= (1 << offset_val2);
+ break;
+ default:
+ return -EINVAL;
2: a5696ca3c14f ! 4: e23e6cb26b92 iio: afe: rescale: reduce risk of integer overflow
@@ drivers/iio/afe/iio-rescale.c: static int rescale_read_raw(struct iio_dev *indio
+ tmp = (s64)*val * rescale->numerator;
+ tmp2 = (s64)*val2 * rescale->denominator;
+ factor = gcd(tmp, tmp2);
-+ *val = tmp / factor;
-+ *val2 = tmp2 / factor;
++ do_div(tmp, factor);
++ *val = tmp;
++ do_div(tmp2, factor);
++ *val2 = tmp2;
return ret;
case IIO_VAL_INT:
*val *= rescale->numerator;
3: 2b435a2f58e8 ! 5: 28203b672942 iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support
@@ drivers/iio/afe/iio-rescale.c: static int rescale_read_raw(struct iio_dev *indio
*val = tmp;
return ret;
+ case IIO_VAL_INT_PLUS_NANO:
-+ fallthrough;
+ case IIO_VAL_INT_PLUS_MICRO:
+ tmp = (s64)*val * rescale->numerator;
+ *val = div_s64(tmp, rescale->denominator);
4: 577020b8326b ! 6: a6c944ae0f99 iio: afe: rescale: add offset support
@@ drivers/iio/afe/iio-rescale.c: static int rescale_read_raw(struct iio_dev *indio
+ * 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:
++ * 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) {
@@ drivers/iio/afe/iio-rescale.c: static int rescale_read_raw(struct iio_dev *indio
+ 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;
++ if (ret != IIO_VAL_INT)
++ return ret < 0 ? ret : -EOPNOTSUPP;
+ }
+
+ ret = iio_read_channel_scale(rescale->source, &scale, &scale2);
@@ drivers/iio/afe/iio-rescale.c: static int rescale_read_raw(struct iio_dev *indio
+ 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:
5: 0add5863ff00 = 7: cc5eb96512d5 iio: afe: rescale: add RTD temperature sensor support
6: 0306e16020d4 = 8: d8aa257aad35 iio: afe: rescale: add temperature transducers
7: 6906c5a21861 ! 9: f038d6a08ea2 dt-bindings: iio: afe: add bindings for temperature-sense-rtd
@@ Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml (new)
+ Channel node of a voltage io-channel.
+
+ '#io-channel-cells':
-+ const: 1
++ const: 0
+
+ excitation-current-microamp:
+ description: The current fed through the RTD sensor.
@@ Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml (new)
+ - |
+ pt1000_1: temperature-sensor0 {
+ compatible = "temperature-sense-rtd";
-+ #io-channel-cells = <1>;
++ #io-channel-cells = <0>;
+ io-channels = <&temp_adc1 0>;
+
+ excitation-current-microamp = <1000>; /* i = U/R = 5 / 5000 */
@@ Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml (new)
+ r-naught-ohms = <1000>;
+ };
+...
-
- ## MAINTAINERS ##
-@@ MAINTAINERS: F: Documentation/devicetree/bindings/iio/afe/current-sense-shunt.yaml
- F: Documentation/devicetree/bindings/iio/afe/voltage-divider.yaml
- F: drivers/iio/afe/iio-rescale.c
-
-+IIO UNIT CONVERTER (TEMPERATURE)
-+M: Liam Beguin <liambeguin@gmail.com>
-+R: Peter Rosin <peda@axentia.se>
-+L: linux-iio@vger.kernel.org
-+S: Maintained
-+F: Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml
-+
- IKANOS/ADI EAGLE ADSL USB DRIVER
- M: Matthieu Castet <castet.matthieu@free.fr>
- M: Stanislaw Gruszka <stf_xl@wp.pl>
8: ac8d4eef179b ! 10: 1db42cb25254 dt-bindings: iio: afe: add bindings for temperature transducers
@@ Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml (new)
+ Channel node of a voltage io-channel.
+
+ '#io-channel-cells':
-+ const: 1
++ const: 0
+
+ sense-offset-millicelsius:
+ description: |
@@ Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml (new)
+ - |
+ ad950: temperature-sensor-0 {
+ compatible = "temperature-transducer";
-+ #io-channel-cells = <1>;
++ #io-channel-cells = <0>;
+ io-channels = <&temp_adc 3>;
+
+ sense-offset-millicelsius = <(-273150)>; /* Kelvin to degrees Celsius */
@@ Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml (new)
+ - |
+ znq_tmp: temperature-sensor-1 {
+ compatible = "temperature-transducer";
-+ #io-channel-cells = <1>;
++ #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 */
+ };
+...
-
- ## MAINTAINERS ##
-@@ MAINTAINERS: R: Peter Rosin <peda@axentia.se>
- L: linux-iio@vger.kernel.org
- S: Maintained
- F: Documentation/devicetree/bindings/iio/afe/temperature-sense-rtd.yaml
-+F: Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml
-
- IKANOS/ADI EAGLE ADSL USB DRIVER
- M: Matthieu Castet <castet.matthieu@free.fr>

base-commit: 6cbb3aa0f9d5d23221df787cf36f74d3866fdb78
--
2.30.1.489.g328c10930387

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