[PATCH v4 0/4] iio: cdc: add Texas Instruments FDC1004 driver

[Victor Chernyakin]

This series adds support for the FDC1004 4-channel I2C capacitive sensor.
This sensor can report single-ended measurements of any one of its
channels, as well as differential measurements between any pair
of them. It has a measurement range of +-15 pF and a resolution of 0.5 fF.

Patch 1 prepares iio_format_value to handle IIO_VAL_DECIMAL64_* formats
introduced in Patch 2.
Patch 2 adds higher-precision IIO_VAL_DECIMAL64_* formats, used
in the driver.
Patch 3 adds the devicetree bindings.
Patch 4 adds the driver itself.

Tested with the sensor connected over an i2c-tiny-usb adapter.

---
Changes in v4:
- Patch 1
  - Moved the floor(log10(S64_MAX)) constant to iio.h, renamed it to IIO_INTLOG10_S64_MAX
  - Added corresponding floor(log10(U64_MAX)) constant

- Patch 4
  - Added "select REGMAP_I2C" to Kconfig
  - Style/whitespace tweaks

- Link to v3: https://lore.kernel.org/SN1PR12MB252882C0E885BF3368E036E5A5612@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

---
Changes in v3:

Split Patch 1 into two patches.

- Patch 1
  - Expanded the comment above abs_s64_no_overflow()

- Patch 4 (previously Patch 3)
  - Added comment on what a negative capacitance bias is used for
  - Reduced some line lengths by introducing a variable with a short name
  - Joined consecutive assignments into single ones
  - Fixed indentation

- Link to v2: https://lore.kernel.org/SN1PR12MB2528DD1E6067CC4C0B76746FA5622@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/

---
Changes in v2:
- Patch 1
  - Added tests
  - Fixed overflow in iio_format_value on 10^scale and UB on abs(LLONG_MIN)
- Patch 2
  - Made the power supply mandatory
- Patch 3
  - Switched from direct I2C calls to regmap
  - Added of device table
  - Removed scan indexes
  - Build up complex values incrementally
  - Adjusted list of includes
  - More designed initializers
  - Various style/whitespace tweaks

- Link to v1: https://lore.kernel.org/SN1PR12MB25286BE4E1EA3B75F8E563A9A5652@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

---
Victor Chernyakin (4):
  iio: prepare iio_format_value to handle higher-precision
    IIO_VAL_DECIMAL64_* formats
  iio: add IIO_VAL_DECIMAL64_{ATTO,ZEPTO,YOCTO} formats
  dt-bindings: iio: cdc: add Texas Instruments FDC1004
  iio: cdc: add Texas Instruments FDC1004 driver

 .../bindings/iio/cdc/ti,fdc1004.yaml          |  46 ++
 MAINTAINERS                                   |   6 +
 drivers/iio/cdc/Kconfig                       |  11 +
 drivers/iio/cdc/Makefile                      |   1 +
 drivers/iio/cdc/fdc1004.c                     | 490 ++++++++++++++++++
 drivers/iio/industrialio-core.c               |  30 +-
 drivers/iio/test/iio-test-format.c            |  16 +
 include/linux/iio/iio.h                       |   3 +
 include/linux/iio/types.h                     |   3 +
 9 files changed, 602 insertions(+), 4 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/iio/cdc/ti,fdc1004.yaml
 create mode 100644 drivers/iio/cdc/fdc1004.c

-- 
2.53.0