iio: adc: ad7944: add driver for AD7944/AD7985/AD7986

This adds a driver for the Analog Devices Inc. AD7944, AD7985, and
AD7986 ADCs. These are a family of pin-compatible ADCs that can sample
at rates up to 2.5 MSPS.

The initial driver adds support for sampling at lower rates using the
usual IIO triggered buffer and can handle all 3 possible reference
voltage configurations.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20240304-ad7944-mainline-v5-2-f0a38cea8901@baylibre.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

MAINTAINERS

@@ -448,6 +448,7 @@ R:	David Lechner <dlechner@baylibre.com>
 S:	Supported
 W:	https://ez.analog.com/linux-software-drivers
 F:	Documentation/devicetree/bindings/iio/adc/adi,ad7944.yaml
+F:	drivers/iio/adc/ad7944.c
 
 ADAFRUIT MINI I2C GAMEPAD
 M:	Anshul Dalal <anshulusr@gmail.com>

drivers/iio/adc/Kconfig

@@ -281,6 +281,16 @@ config AD7923
 	  To compile this driver as a module, choose M here: the
 	  module will be called ad7923.
 
+config AD7944
+	tristate "Analog Devices AD7944 and similar ADCs driver"
+	depends on SPI
+	help
+	  Say yes here to build support for Analog Devices
+	  AD7944, AD7985, AD7986 ADCs.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called ad7944
+
 config AD7949
 	tristate "Analog Devices AD7949 and similar ADCs driver"
 	depends on SPI

drivers/iio/adc/Makefile

@@ -29,6 +29,7 @@ obj-$(CONFIG_AD7780) += ad7780.o
 obj-$(CONFIG_AD7791) += ad7791.o
 obj-$(CONFIG_AD7793) += ad7793.o
 obj-$(CONFIG_AD7887) += ad7887.o
+obj-$(CONFIG_AD7944) += ad7944.o
 obj-$(CONFIG_AD7949) += ad7949.o
 obj-$(CONFIG_AD799X) += ad799x.o
 obj-$(CONFIG_AD9467) += ad9467.o