[PATCH v4 0/2] iio: adc: Add support for Texas Instruments ADS112C04

[Kyle Hsieh <kylehsieh1995@gmail.com>]

This patch series introduces support for the Texas Instruments ADS112C04
Analog-to-Digital Converters.

The ADS112C04 (16-bit) is precision, low-power, delta-sigma ADCs with
an I2C interface. They feature a flexible input multiplexer supporting
single-ended and differential measurements, a programmable gain amplifier,
and an internal voltage reference.

Note: While this chip shares similarities with the ADS112C14 (currently 
being upstreamed by David Lechner), the register maps and feature sets 
are sufficiently different to warrant a separate driver. However, the
DT bindings and channel parsing logic have been aligned with the
ADS112C14 conventions.

This initial submission provides a minimal feature set (single-shot 
conversions and basic DRDY interrupt) covering current use cases.

Signed-off-by: Kyle Hsieh <kylehsieh1995@gmail.com>
---
Changes in v4:
- dt-bindings: iio: adc: ti,ads112c04:
  - Fixed excitation-current-nanoamp to use single-entry list syntax
    (items: - enum: [...]) instead of combining maxItems: 1 with a
    mapping-style items, which failed dt_binding_check.
  - Widened excitation-channels to maximum: 5 to account for IDAC1/
    IDAC2 also being routable to REFP0/REFN0, and documented the
    mapping, per David Lechner.
  - Reduced excitation-current-nanoamp to a single entry, since the
    two IDAC outputs share one current setting, per David Lechner.
  - Changed burn-out-current-nanoamp to use `const: 10000`, per David
    Lechner.
  - Renamed reference-sources' internal enum value to "internal"
    (dropped voltage suffix, since there is only one internal
    reference), per David Lechner.

- iio: adc: ti-ads112c04:
  - Fixed word-read byte ordering by switching to
    i2c_smbus_read_word_swapped(), addressing a big-endian data
    corruption issue flagged by Sashiko AI review.
  - Masked the DRDY interrupt in the hardirq handler
    (disable_irq_nosync()) and re-enabled it once the conversion data
    is read, to avoid an interrupt storm on level-triggered DRDY
    configurations, without hardcoding the trigger type.
  - Reworked reference-sources handling in parse_channels(): it is now
    validated against the actually-selected refp-supply instead of
    being unconditionally rejected, per David Lechner.
  - Simplified regulator handling in probe() using
    devm_regulator_get_enable_read_voltage(), dropping the now-unused
    vref_reg field, per David Lechner.
  - Corrected the commit message to no longer claim refn-supply
    support, since it remains explicitly unsupported in probe().
- Added a MAINTAINERS entry for the new binding and driver.
- Link to v3: https://lore.kernel.org/r/20260805-ti-ads112c04-driver-v3-0-49f436829e01@gmail.com

Changes in v3:
- dt-bindings: iio: adc: ti,ads112c04:
  - Resolved dt_binding_check errors by removing redundant $ref for
    standard unit suffixes and fixing YAML array syntax.
  - Added full hardware capability descriptions (excitation-channels,
    excitation-current-nanoamp, burn-out-current-nanoamp,
    reference-sources) as suggested by David Lechner.
  - Restricted the reg maximum to 11 and updated the regex to
    ^channel@[0-9a-b]$ to accurately reflect the 12 possible MUX
    combinations.

- iio: adc: ti-ads112c04:
  - Transitioned all I2C read/write wrappers to use SMBus APIs
    (i2c_smbus_read_byte_data, i2c_smbus_read_word_data, etc.) to
    gracefully handle I2C errors, NACKs, and Repeated Starts, addressing
    feedback from Joshua Crofts and Jonathan Cameron.
  - Added forward compatibility checks in probe() and parse_channels()
    using dev_err_probe() to return -EOPNOTSUPP for unimplemented DT
    properties.
  - Reverted devm_request_irq() flags to 0 to let the driver inherit the
    trigger type strictly from the DT, per Jonathan Cameron's advice.
  - Reduced the data wait timeout to 100ms, reflecting the chip's slowest
    data rate of 20 SPS.
  - Fixed #include alphabetical sorting, grouped <linux/iio/*> headers,
    and added missing headers.
  - Fixed variable declaration ordering (reverse xmas tree) and updated
    variable naming to vref_mV (SI unit exception).
  - Optimized GPIO reset logic using GPIOD_OUT_HIGH.
- Link to v2: https://lore.kernel.org/r/20260731-ti-ads112c04-driver-v2-0-aab0168c3c01@gmail.com

Changes in v2:
- Replaced `vref-supply` with `refp-supply` and `refn-supply` to accurately reflect hardware.
- Refactored the driver to dynamically parse channel configurations and routing from DT child nodes.
- Modernized the driver using kernel macros.
- Handled endianness elegantly.
- Added hardware reset fallback logic.
- Inherited IRQ trigger type from device tree instead of hardcoding.
- Fixed a bug where the MUX software cache could desync from hardware if the I2C write failed.
- Added strict return value checking for all I2C writes during probe.
- Updated the `i2c_device_id` array to use C99 named initializers.
- Link to v1: https://lore.kernel.org/r/20260728-ti-ads112c04-driver-v1-0-475efe4e2b78@gmail.com

---
Kyle Hsieh (2):
      dt-bindings: iio: adc: ti,ads112c04: Add binding for ADS112C04
      iio: adc: ti-ads112c04: Add support for TI ADS112C04

 .../devicetree/bindings/iio/adc/ti,ads112c04.yaml  | 148 +++++++
 MAINTAINERS                                        |   7 +
 drivers/iio/adc/Kconfig                            |  10 +
 drivers/iio/adc/Makefile                           |   1 +
 drivers/iio/adc/ti-ads112c04.c                     | 425 +++++++++++++++++++++
 5 files changed, 591 insertions(+)
---
base-commit: 350d1fb9204b13c5f95e511e98b8bcb47574d425
change-id: 20260724-ti-ads112c04-driver-be7e89047834

Best regards,
-- 
Kyle Hsieh <kylehsieh1995@gmail.com>