iio: adc: ad4130: add AD4130 driver

AD4130-8 is an ultra-low power, high precision, measurement solution for
low bandwidth battery operated applications.

The fully integrated AFE (Analog Front-End) includes a multiplexer for up
to 16 single-ended or 8 differential inputs, PGA (Programmable Gain
Amplifier), 24-bit Sigma-Delta ADC, on-chip reference and oscillator,
selectable filter options, smart sequencer, sensor biasing and excitation
options, diagnostics, and a FIFO buffer.

Signed-off-by: Cosmin Tanislav <cosmin.tanislav@analog.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20221021104115.1812486-3-demonsingur@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/ABI/testing/sysfs-bus-iio-adc-ad4130

@@ -0,0 +1,36 @@
+What:		/sys/bus/iio/devices/iio:deviceX/in_voltage-voltage_filter_mode_available
+KernelVersion:  6.2
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Reading returns a list with the possible filter modes.
+		"sinc4"       - Sinc 4. Excellent noise performance. Long 1st
+				conversion time. No natural 50/60Hz rejection.
+		"sinc4+sinc1" - Sinc4 + averaging by 8. Low 1st conversion time.
+		"sinc3"	      - Sinc3. Moderate 1st conversion time. Good noise
+				performance.
+		"sinc3+rej60" - Sinc3 + 60Hz rejection. At a sampling frequency
+				of 50Hz, achieves simultaneous 50Hz and 60Hz
+				rejection.
+		"sinc3+sinc1" - Sinc3 + averaging by 8. Low 1st conversion time.
+				Best used with a sampling frequency of at least
+				216.19Hz.
+		"sinc3+pf1"   - Sinc3 + Post Filter 1.
+				53dB rejection @ 50Hz, 58dB rejection @ 60Hz.
+		"sinc3+pf2"   - Sinc3 + Post Filter 2.
+				70dB rejection @ 50Hz, 70dB rejection @ 60Hz.
+		"sinc3+pf3"   - Sinc3 + Post Filter 3.
+				99dB rejection @ 50Hz, 103dB rejection @ 60Hz.
+		"sinc3+pf4"   - Sinc3 + Post Filter 4.
+				103dB rejection @ 50Hz, 109dB rejection @ 60Hz.
+
+What:		/sys/bus/iio/devices/iio:deviceX/in_voltageY-voltageZ_filter_mode
+KernelVersion:  6.2
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Set the filter mode of the differential channel. When the filter
+		mode changes, the in_voltageY-voltageZ_sampling_frequency and
+		in_voltageY-voltageZ_sampling_frequency_available attributes
+		might also change to accommodate the new filter mode.
+		If the current sampling frequency is out of range for the new
+		filter mode, the sampling frequency will be changed to the
+		closest valid one.

MAINTAINERS

@@ -1122,7 +1122,9 @@ M:	Cosmin Tanislav <cosmin.tanislav@analog.com>
 L:	linux-iio@vger.kernel.org
 S:	Supported
 W:	http://ez.analog.com/community/linux-device-drivers
+F:	Documentation/ABI/testing/sysfs-bus-iio-adc-ad4130
 F:	Documentation/devicetree/bindings/iio/adc/adi,ad4130.yaml
+F:	drivers/iio/adc/ad4130.c
 
 ANALOG DEVICES INC AD7192 DRIVER
 M:	Alexandru Tachici <alexandru.tachici@analog.com>

drivers/iio/adc/Kconfig

@@ -21,6 +21,20 @@ config AD_SIGMA_DELTA
 	select IIO_BUFFER
 	select IIO_TRIGGERED_BUFFER
 
+config AD4130
+	tristate "Analog Device AD4130 ADC Driver"
+	depends on SPI
+	select IIO_BUFFER
+	select IIO_KFIFO_BUF
+	select REGMAP_SPI
+	depends on COMMON_CLK
+	help
+	  Say yes here to build support for Analog Devices AD4130-8 SPI analog
+	  to digital converters (ADC).
+
+	  To compile this driver as a module, choose M here: the module will be
+	  called ad4130.
+
 config AD7091R5
 	tristate "Analog Devices AD7091R5 ADC Driver"
 	depends on I2C

drivers/iio/adc/Makefile

@@ -6,6 +6,7 @@
 # When adding new entries keep the list in alphabetical order
 obj-$(CONFIG_AB8500_GPADC) += ab8500-gpadc.o
 obj-$(CONFIG_AD_SIGMA_DELTA) += ad_sigma_delta.o
+obj-$(CONFIG_AD4130) += ad4130.o
 obj-$(CONFIG_AD7091R5) += ad7091r5.o ad7091r-base.o
 obj-$(CONFIG_AD7124) += ad7124.o
 obj-$(CONFIG_AD7192) += ad7192.o