[PATCH v7 00/13] iio: afe: add temperature rescaling support

From: Liam Beguin
Date: Sun Aug 01 2021 - 15:40:15 EST

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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 few
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.

As Jonathan suggested, I also started a Kunit test suite for the
iio-rescale driver.
Adding these test cases, I found that the IIO_VAL_FRACTIONAL_LOG2
rescaling wasn't as precise as expected so I tried to fix that as well.

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

Thanks for your time

Liam Beguin (13):
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: expose scale processing function
iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support
iio: afe: rescale: add offset support
iio: afe: rescale: reduce risk of integer overflow
iio: afe: rescale: fix precision on fractional log scale
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 | 271 ++++++++--
drivers/iio/inkern.c | 40 +-
drivers/iio/test/Kconfig | 10 +
drivers/iio/test/Makefile | 1 +
drivers/iio/test/iio-test-rescale.c | 483 ++++++++++++++++++
include/linux/iio/afe/rescale.h | 34 ++
8 files changed, 1010 insertions(+), 44 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 v6:
1: 16627ca44022 < -: ------------ iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support
-: ------------ > 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
-: ------------ > 3: ed0721fb6bd1 iio: inkern: make a best effort on offset calculation
-: ------------ > 4: f8fb78bb1112 iio: afe: rescale: expose scale processing function
-: ------------ > 5: 014363f5f703 iio: afe: rescale: add INT_PLUS_{MICRO,NANO} support
2: dec2a933fbf3 = 6: e4e3bcd752dd iio: afe: rescale: add offset support
4: f2f4af324d5d ! 7: 23efde61c576 iio: afe: rescale: reduce risk of integer overflow
@@ drivers/iio/afe/iio-rescale.c
- unsigned long long tmp;
+ s64 tmp, tmp2;
+ u32 factor;
+ u32 mult;
+ u32 rem;
+ u32 neg;

switch (scale_type) {
case IIO_VAL_FRACTIONAL:
@@ drivers/iio/afe/iio-rescale.c
+ check_mul_overflow(*val2, rescale->denominator, (s32 *)&tmp2)) {
+ tmp = (s64)*val * rescale->numerator;
+ tmp2 = (s64)*val2 * rescale->denominator;
-+ factor = gcd(tmp, tmp2);
++ factor = gcd(abs(tmp), abs(tmp2));
+ tmp = div_s64(tmp, factor);
+ tmp2 = div_s64(tmp2, factor);
+ }
5: 4a8d77501f32 ! 8: e16f69d61f09 iio: afe: rescale: fix precision on fractional log scale
@@ drivers/iio/afe/iio-rescale.c: int rescale_process_scale(struct rescale *rescale
- do_div(tmp, rescale->denominator);
- tmp *= rescale->numerator;
- do_div(tmp, 1000000000LL);
-- *val = tmp;
++ if (check_mul_overflow(*val, rescale->numerator, (s32 *)&tmp) ||
++ check_mul_overflow(rescale->denominator, (1 << *val2), (s32 *)&tmp2)) {
++ tmp = (s64)*val * rescale->numerator;
++ tmp2 = (s64)rescale->denominator * (1 << *val2);
++ factor = gcd(abs(tmp), abs(tmp2));
++ tmp = div_s64(tmp, factor);
++ tmp2 = div_s64(tmp2, factor);
++ }
+ *val = tmp;
- return scale_type;
-+ *val = rescale->numerator * *val;
-+ *val2 = rescale->denominator * (1 << *val2);
++ *val2 = tmp2;
+ return IIO_VAL_FRACTIONAL;
case IIO_VAL_INT_PLUS_NANO:
- tmp = ((s64)*val * 1000000000LL + *val2) * rescale->numerator;
- tmp = div_s64(tmp, rescale->denominator);
+ case IIO_VAL_INT_PLUS_MICRO:
+ if (scale_type == IIO_VAL_INT_PLUS_NANO)
3: 60bd09555300 ! 9: 88ad312c5a1b iio: test: add basic tests for the iio-rescale driver
@@ drivers/iio/test/Kconfig
# Keep in alphabetical order
+config IIO_RESCALE_KUNIT_TEST
+ bool "Test IIO rescale conversion functions"
-+ depends on KUNIT=y
++ depends on KUNIT && !IIO_RESCALE
+ default KUNIT_ALL_TESTS
+ help
+ If you want to run tests on the iio-rescale code say Y here.
@@ drivers/iio/test/iio-test-rescale.c (new)
+ .denominator = 8060,
+ .schan_scale_type = IIO_VAL_INT_PLUS_NANO,
+ .schan_val = 10,
++ .schan_val2 = 123456,
++ .expected = "1240.710106203\n",
++ },
++ {
++ .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\n",
++ },
++ {
++ .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 = "1240.847890\n",
++ },
++ {
++ .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 = "-1240.847890\n",
++ },
++ /*
++ * INT_PLUS_{MICRO,NANO} positive/negative corner cases
++ */
++ {
++ .name = "typical 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\n",
++ },
++ {
++ .name = "typical 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\n",
++ },
++ {
++ .name = "typical 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\n",
++ },
++ {
++ .name = "typical 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\n",
++ },
++ {
++ .name = "typical 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\n",
++ },
++ /*
++ * 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 = "1256.012008560\n",
+ },
+ {
-+ .name = "typical IIO_VAL_INT_PLUS_NANO, negative",
++ .name = "decimal overflow IIO_VAL_INT_PLUS_NANO, negative",
+ .numerator = -1000000,
+ .denominator = 8060,
+ .schan_scale_type = IIO_VAL_INT_PLUS_NANO,
@@ drivers/iio/test/iio-test-rescale.c (new)
+ .expected = "-1256.012008560\n",
+ },
+ {
-+ .name = "typical IIO_VAL_INT_PLUS_MICRO, positive",
++ .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 = "-1256.012008560\n",
++ },
++ {
++ .name = "decimal overflow IIO_VAL_INT_PLUS_MICRO, positive",
+ .numerator = 1000000,
+ .denominator = 8060,
+ .schan_scale_type = IIO_VAL_INT_PLUS_MICRO,
@@ drivers/iio/test/iio-test-rescale.c (new)
+ .expected = "16557.914267\n",
+ },
+ {
-+ .name = "typical IIO_VAL_INT_PLUS_MICRO, negative",
++ .name = "decimal overflow IIO_VAL_INT_PLUS_MICRO, negative",
+ .numerator = -1000000,
+ .denominator = 8060,
+ .schan_scale_type = IIO_VAL_INT_PLUS_MICRO,
@@ drivers/iio/test/iio-test-rescale.c (new)
+ .schan_val2 = 123456789,
+ .expected = "-16557.914267\n",
+ },
++ {
++ .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\n",
++ },
+ /*
+ * 32-bit overflow conditions
+ */
@@ drivers/iio/test/iio-test-rescale.c (new)
+ .expected = "-214748364.700000000\n",
+ },
+ {
++ .name = "overflow IIO_VAL_FRACTIONAL_LOG2, positive",
++ .numerator = 0x7FFFFFFF,
++ .denominator = 53,
++ .schan_scale_type = IIO_VAL_FRACTIONAL_LOG2,
++ .schan_val = 4096,
++ .schan_val2 = 16,
++ .expected = "2532409.961084905\n",
++ },
++ {
++ .name = "overflow IIO_VAL_FRACTIONAL_LOG2, negative",
++ .numerator = 0x7FFFFFFF,
++ .denominator = 53,
++ .schan_scale_type = IIO_VAL_FRACTIONAL_LOG2,
++ .schan_val = -4096,
++ .schan_val2 = 16,
++ .expected = "-2532409.961084905\n",
++ },
++ {
+ .name = "overflow IIO_VAL_INT_PLUS_NANO, positive",
+ .numerator = 2,
+ .denominator = 20,
@@ drivers/iio/test/iio-test-rescale.c (new)
+ .expected = "-1.214748364\n",
+ },
+ {
++ .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 = 0x7fffffff,
++ .expected = "-1.214748364\n",
++ },
++ {
+ .name = "overflow IIO_VAL_INT_PLUS_MICRO, positive",
+ .numerator = 2,
+ .denominator = 20,
@@ drivers/iio/test/iio-test-rescale.c (new)
+ .schan_val2 = 0x7fffffff,
+ .expected = "-215.748364\n",
+ },
++ {
++ .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 = 0x7fffffff,
++ .expected = "-215.748364\n",
++ },
+};
+
+const struct rescale_tc_data offset_cases[] = {
6: 2b6e4f47c974 = 10: 2c4a31e62c31 iio: afe: rescale: add RTD temperature sensor support
7: 715e1877e30f = 11: d1258a38d194 iio: afe: rescale: add temperature transducers
8: 0bc8546f13e5 = 12: 01fa34bf5362 dt-bindings: iio: afe: add bindings for temperature-sense-rtd
9: 4bc54afa3e94 ! 13: 107e61e09eec dt-bindings: iio: afe: add bindings for temperature transducers
@@ Commit message
through a temperature transducer (either voltage or current).

Signed-off-by: Liam Beguin <lvb@xxxxxxxxxx>
+ Reviewed-by: Rob Herring <robh@xxxxxxxxxx>

## Documentation/devicetree/bindings/iio/afe/temperature-transducer.yaml (new) ##
@@

base-commit: 6cbb3aa0f9d5d23221df787cf36f74d3866fdb78
--
2.30.1.489.g328c10930387

Next message: Liam Beguin: "[PATCH v7 01/13] iio: inkern: apply consumer scale on IIO_VAL_INT cases"
Previous message: Dario Binacchi: "Re: [RESEND PATCH v4] clk: stm32f4: fix post divisor setup for I2S/SAI PLLs"
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