[PATCH v4 0/3] hwmon: (lm75) add MAX31875 support

[John Erasmus Mari Geronimo]

Add support for the Analog Devices MAX31875 I2C temperature sensor by
extending the existing lm75 driver.

The MAX31875 provides a 16-bit configuration register, selectable
resolution of 8, 9, 10, or 12 bits, conversion rates of 125 ms, 250 ms,
1 s, or 4 s, and an alarm output.

Changes since v3:
- driver: skip the alert polarity configuration for the MAX31875. It has
  no polarity bit, and the bit used for 16-bit chips is part of its
  conversion rate field.
- driver: set the default resolution and conversion rate at probe so the
  driver state matches the chip.
- The conversion rate field is D2:D1 of the configuration register (see
  the datasheet's Configuration Register Definition). It is read here as
  0x0600 because the driver reads this register without byte swapping.

Tested on a Raspberry Pi 4B with a MAX31875: defaults are restored at
probe after the chip is set to 12-bit/125 ms, update_interval selects
each of the four conversion rates without changing the resolution, and
temp1_alarm follows temp1_max. This was run on the Raspberry Pi 6.12
tree, which reads the configuration register byte-swapped, so the
equivalent bit positions were used there.

Changes since v2:
- dt-bindings: expand the commit message to explain why the MAX31875
  needs its own compatible string instead of reusing an existing
  lm75-family one, and pick up Conor Dooley's Acked-by given
  conditional on that fix.
- driver: drop the .resolutions table, which incorrectly tied
  resolution to the sample-time index even though the two are
  independently configurable on this chip (Guenter Roeck).
- driver: use the BIT() idiom for the alarm bit read to match the
  rest of the file (Guenter Roeck).

Changes since v1:
- Rework the implementation to use the existing lm75 driver instead of
  the previously selected max31827 base driver.
- Add the MAX31875 Device Tree binding, documentation, and driver
  configuration for resolution, conversion rate, and alarm reporting.

John Erasmus Mari Geronimo (3):
  dt-bindings: hwmon: lm75: add MAX31875
  hwmon: (lm75) add MAX31875 documentation
  hwmon: (lm75) add MAX31875 support

 .../devicetree/bindings/hwmon/lm75.yaml       |  1 +
 Documentation/hwmon/lm75.rst                  |  6 ++--
 drivers/hwmon/Kconfig                         |  2 +-
 drivers/hwmon/lm75.c                          | 30 ++++++++++++++++++-
 4 files changed, 35 insertions(+), 4 deletions(-)

-- 
2.34.1