Add support for AD5706R DAC

This series adds support for the Analog Devices AD5706R, a 4-channel
16-bit current output digital-to-analog converter with SPI interface.

This initial driver provides basic DAC functionality through standard
IIO interfaces.

Datasheet: https://www.analog.com/en/products/ad5706r.html

Signed-off-by: Alexis Czezar Torreno <alexisczezar.torreno@analog.com>
---
Changes in v9:
- Kconfig: changed REGMAP_SPI to REGMAP
- updated cover letter and driver commit message
- Link to v8: https://lore.kernel.org/r/20260417-dev_ad5706r-v8-0-ef87d...

Changes in v8:
- driver:
  - changed DAC_CODE from BIT(16) to GENMASK(15,0)
  - removed defines for single/multi byte, replaced with number
  - adjusted regmap_write to use if/else similar to read()
  - reverted in_range back to open code equivalent, removed minmax.h
- Link to v7: https://lore.kernel.org/r/20260410-dev_ad5706r-v7-0-af93a...

Changes in v7:
- driver:
  - Moved/added size validation before data access in write()/read()
- Link to v6: https://lore.kernel.org/r/20260410-dev_ad5706r-v6-0-f3fda...

Changes in v6:
- driver:
  - Added size validation in regmap_write()
  - Used &st->tx_buf[0] consistently in _be32/be16 calls
  - Added missing indent in AD5706R_CHAN
- Link to v5: https://lore.kernel.org/r/20260407-dev_ad5706r-v5-0-a4c77...

Changes in v5:
- dt-bindings:
  - Changed out-en-gpios to enable-gpios
- driver:
  - Kconfig: Added select REGMAP_SPI
  - Headers: Removed device.h, errno.h, string.h; added dev_printk.h
  - Use IIO_DMA_MINALIGN instead of ARCH_DMA_MINALIGN
  - Replaced memcpy/memset with put_unaligned_be* for consistency
  - Added struct device *dev shorthand in probe()
  - other minor style edits
- Link to v4: https://lore.kernel.org/r/20260401-dev_ad5706r-v4-0-a7851...

Changes in v4:
- dt-bindings:
  - Reverted pwm and gpio entries.
  - Added missing power supply properties
  - Clocks not added back as they were driver specific, not device
    properties
- driver:
  - Added missing includes
  - Converted to use regmap with custom SPI bus implementation.
    spi_write_then_read not applied as suggested, prevents future
    need to change SPI speed
  - removed driver speciifc mutex/guards in favor of regmap internal
    locking
  - Minor style cleanups
- Link to v3: https://lore.kernel.org/r/20260318-dev_ad5706r-v3-0-5d078...

Changes in v3:
- Added MAINTAINERS entry, files added on each patch
- dt-bindings:
  - Added allOf and ref to spi-peripheral-props.yaml
  - Changed additionalProperties to unevaluatedProperties
  - Added avdd-supply property and added it to required
- driver:
  - Removed redundant includes, added respective includes of APIs used
  - Simplified bit manipulation in SPI read/write, used feedback from v2
  - Fixed inconsistent trailing commas in device ID tables
  - Removed zero initialization in spi_device_id
- Link to v2: https://lore.kernel.org/r/20260311-dev_ad5706r-v2-0-f3670...

Changes in v2:
- Stripped driver down to basic DAC functionality (read/write raw,
  read-only scale) as suggested.
- Removed PWM (LDAC), GPIO (reset/shutdown), clock generator,
  SPI engine frequency switching, debugfs streaming, and all
  custom ext_info sysfs attributes
- Removed regmap, IIO_BUFFER, and iio/sysfs.h dependencies
- Simplified SPI read/write to use standard spi_sync_transfer
  without clock mode logic
- Scale reports default 50mA range as read-only using
  IIO_VAL_FRACTIONAL_LOG2; writable range selection deferred
  to future follow-up series
- Simplified DT binding to only require compatible, reg, and
  spi-max-frequency
- Link to v1: https://lore.kernel.org/r/20260220-dev_ad5706r-v1-0-7253b...

---
Alexis Czezar Torreno (2):
      dt-bindings: iio: dac: Add ADI AD5706R
      iio: dac: ad5706r: Add support for AD5706R DAC

 .../devicetree/bindings/iio/dac/adi,ad5706r.yaml   | 105 +++++++++
 MAINTAINERS                                        |   8 +
 drivers/iio/dac/Kconfig                            |  11 +
 drivers/iio/dac/Makefile                           |   1 +
 drivers/iio/dac/ad5706r.c                          | 253 +++++++++++++++++++++
 5 files changed, 378 insertions(+)
---
base-commit: 3674f3ca92730d9a07b42b311f1337d83c4d5605
change-id: 20260220-dev_ad5706r-2105e1dd29ab

Best regards,
-- 
Alexis Czezar Torreno <alexisczezar.torreno@analog.com>