Add support for the AD4880, a dual-channel 20-bit 40MSPS SAR ADC from
the same family as AD4080.

The AD4880 has two independent ADC channels, each with its own SPI
configuration interface and LVDS data output. The driver uses
spi_new_ancillary_device() for the second channel's SPI and requires
two io-backend instances for the data interfaces.

This series includes:
  - SPI core fix to allow ancillary devices to share parent's chip selects
  - New devm_iio_backend_get_by_index() helper for multi-channel backend lookup
  - DT bindings update for AD4880
  - Driver support for AD4880

Datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/ad4880.pdf

Antoniu Miclaus (4):
  spi: allow ancillary devices to share parent's chip selects
  iio: backend: add devm_iio_backend_get_by_index()
  dt-bindings: iio: adc: ad4080: add AD4880 support
  iio: adc: ad4080: add support for AD4880 dual-channel ADC

 .../bindings/iio/adc/adi,ad4080.yaml          |  51 +++-
 drivers/iio/adc/ad4080.c                      | 256 ++++++++++++++----
 drivers/iio/industrialio-backend.c            |  51 ++++
 drivers/spi/spi.c                             |  29 +-
 include/linux/iio/backend.h                   |   2 +
 5 files changed, 330 insertions(+), 59 deletions(-)

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2.43.0