[PATCH v4 0/2] Add support for Analog Devices MAX30210

[John Erasmus Mari Geronimo <johnerasmusmari.geronimo@analog.com>]

This series adds support for the Analog Devices MAX30210 I2C
temperature sensor.

The device provides a 16-bit temperature output and includes
features such as a hardware FIFO, programmable sampling rate,
threshold alarms, and interrupt support. These capabilities map
naturally to the IIO subsystem, particularly the buffered interface
and event framework -- hwmon has no equivalent buffered-capture
framework, and its alarm attributes are polled rather than
interrupt-driven, so there is no path to supporting the FIFO or the
autonomous threshold comparators there.

Although the MAX30210 belongs to the same device family as the
MAX30208, it is implemented as a separate driver. The MAX30210 has
a significantly different feature set, including a 64-sample hardware
FIFO with configurable watermark interrupts, programmable sampling
rates, and event support. These features require buffered operation
and IRQ-driven data handling which are not present in the MAX30208
driver (which talks to the device directly via i2c_smbus_*() calls
with no regmap, and has no IIO buffer or event interface at all).

In addition, the MAX30210 uses a different register map and a more
flexible I2C address selection scheme. Supporting both devices in a
single driver would introduce substantial conditional logic, so a
separate driver keeps the implementation simpler and easier to
maintain.

Patch 1 adds the devicetree binding.
Patch 2 adds the IIO driver implementation.

Changes since v3:
https://lore.kernel.org/all/cover.1789032019.git.johnerasmusmari.geronimo@analog.com/
- regmap_noinc_read() for FIFO reads instead of regmap_bulk_read(),
  which (combined with regmap caching) could silently return stale
  cached values of unrelated registers instead of real FIFO data.
- Mark both bytes of TEMP_DATA_REG volatile for the same reason.
- Decouple threshold events from the buffer via a refcounted
  autoconv_get()/autoconv_put() pair, so either can be used
  independently or concurrently.
- Don't let a single-shot direct-mode read race with/clobber
  autonomous conversion mode if a threshold event or the buffer is
  already using it -- return -EBUSY instead.
- Don't hard-fail probe when there is no interrupt; fall back to
  direct-mode-only operation.
- Fix devm teardown ordering so an in-flight interrupt can't use a
  freed event interface on removal.
- Re-assert the powerdown GPIO on removal so the device reaches
  standby instead of staying powered indefinitely.
- Style/API fixes from review (register/field grouping, _MASK
  naming, FIELD_PREP/regmap_assign_bits usage, C99 initializers,
  dropped redundant i2c_check_functionality() check, comment
  cleanup).

All of the above have been verified on real MAX30210 hardware
(Raspberry Pi 4 test rig), including the no-IRQ fallback, buffer and
event refcounting (independently and concurrently), rmmod/insmod
under live interrupts, powerdown GPIO assertion on removal, and FIFO
flush correctness.

Changes since v2:
https://lore.kernel.org/all/20260304122509.67931-1-johnerasmusmari.geronimo@analog.com/
- Fix FIFO byte-count handling and sample decoding.
- Fix IIO debug register read/write access.
- Validate event threshold values and sampling-frequency register values.
- Return the correct sampling-frequency format and reject direct reads
  while buffered capture is enabled.
- Clean up the Kconfig entry and device-tree supply declaration.

John Erasmus Mari Geronimo (2):
  dt-bindings: iio: temperature: add ADI MAX30210
  iio: temperature: add support for Analog Devices MAX30210

 .../iio/temperature/adi,max30210.yaml         |  61 ++
 MAINTAINERS                                   |   8 +
 drivers/iio/temperature/Kconfig               |  13 +
 drivers/iio/temperature/Makefile              |   1 +
 drivers/iio/temperature/max30210.c            | 788 ++++++++++++++++++
 5 files changed, 871 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/temperature/adi,max30210.yaml
 create mode 100644 drivers/iio/temperature/max30210.c

-- 
2.34.1