iio: adc: adding support for MCP3564 ADC

This is the iio driver for Microchip family of 153.6 ksps,
Low-Noise 16/24-Bit Delta-Sigma ADCs with an SPI interface
(Microchip's  MCP3461, MCP3462, MCP3464, MCP3461R, MCP3462R,
MCP3464R, MCP3561, MCP3562, MCP3564, MCP3561R,
MCP3562R and MCP3564R analog to digital converters).

Signed-off-by: Marius Cristea <marius.cristea@microchip.com>
Link: https://lore.kernel.org/r/20230829154133.40716-3-marius.cristea@microchip.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/ABI/testing/sysfs-bus-iio-adc-mcp3564

@@ -0,0 +1,53 @@
+What:		/sys/bus/iio/devices/iio:deviceX/boost_current_gain
+KernelVersion:	6.4
+Contact:	linux-iio@vger.kernel.org
+Description:
+		This attribute is used to set the gain of the biasing current
+		circuit of the Delta-Sigma modulator. The different BOOST
+		settings are applied to the entire modulator circuit, including
+		the voltage reference buffers.
+
+What:		/sys/bus/iio/devices/iio:deviceX/boost_current_gain_available
+KernelVersion:	6.4
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Reading returns a list with the possible gain values for
+		the current biasing circuit of the Delta-Sigma modulator.
+
+What:		/sys/bus/iio/devices/iio:deviceX/auto_zeroing_mux_enable
+KernelVersion:	6.4
+Contact:	linux-iio@vger.kernel.org
+Description:
+		This attribute is used to enable the analog input multiplexer
+		auto-zeroing algorithm (the input multiplexer and the ADC
+		include an offset cancellation algorithm that cancels the offset
+		contribution of the ADC). When the offset cancellation algorithm
+		is enabled, ADC takes two conversions, one with the differential
+		input as VIN+/VIN-, one with VIN+/VIN- inverted. In this case the
+		conversion time is multiplied by two compared to the default
+		case where the algorithm is disabled. This technique allows the
+		cancellation of the ADC offset error and the achievement of
+		ultra-low offset without any digital calibration. The resulting
+		offset is the residue of the difference between the two
+		conversions, which is on the order of magnitude of the noise
+		floor. This offset is effectively canceled at every conversion,
+		so the residual offset error temperature drift is extremely low.
+		Write '1' to enable it, write '0' to disable it.
+
+What:		/sys/bus/iio/devices/iio:deviceX/auto_zeroing_ref_enable
+KernelVersion:	6.4
+Contact:	linux-iio@vger.kernel.org
+Description:
+		This attribute is used to enable the chopping algorithm for the
+		internal voltage reference buffer. This setting has no effect
+		when external voltage reference is selected.
+		Internal voltage reference buffer injects a certain quantity of
+		1/f noise into the system that can be modulated with the
+		incoming input signals and can limit the SNR performance at
+		higher Oversampling Ratio values (over 256). To overcome this
+		limitation, the buffer includes an auto-zeroing algorithm that
+		greatly reduces (cancels out) the 1/f noise and cancels the
+		offset value of the reference buffer. As a result, the SNR of
+		the system is not affected by this 1/f noise component of the
+		reference buffer, even at maximum oversampling ratio values.
+		Write '1' to enable it, write '0' to disable it.

MAINTAINERS

@@ -14019,6 +14019,13 @@ S:	Supported
 F:	Documentation/devicetree/bindings/regulator/mcp16502-regulator.txt
 F:	drivers/regulator/mcp16502.c
 
+MICROCHIP MCP3564 ADC DRIVER
+M:      Marius Cristea <marius.cristea@microchip.com>
+L:      linux-iio@vger.kernel.org
+S:      Supported
+F:      Documentation/devicetree/bindings/iio/adc/microchip,mcp3564.yaml
+F:      drivers/iio/adc/mcp3564.c
+
 MICROCHIP MCP3911 ADC DRIVER
 M:	Marcus Folkesson <marcus.folkesson@gmail.com>
 M:	Kent Gustavsson <kent@minoris.se>

drivers/iio/adc/Kconfig

@@ -789,6 +789,19 @@ config MCP3422
 	  This driver can also be built as a module. If so, the module will be
 	  called mcp3422.
 
+config MCP3564
+        tristate "Microchip Technology MCP3461/2/4/R, MCP3561/2/4/R driver"
+        depends on SPI
+        depends on IIO
+        help
+          Say yes here to build support for Microchip Technology's MCP3461,
+          MCP3462, MCP3464, MCP3461R, MCP3462R, MCP3464R, MCP3561, MCP3562,
+          MCP3564, MCP3561R, MCP3562R and MCP3564R analog to digital
+          converters.
+
+          This driver can also be built as a module. If so, the module will be
+          called mcp3564.
+
 config MCP3911
 	tristate "Microchip Technology MCP3911 driver"
 	depends on SPI

drivers/iio/adc/Makefile

@@ -72,6 +72,7 @@ obj-$(CONFIG_MAX77541_ADC) += max77541-adc.o
 obj-$(CONFIG_MAX9611) += max9611.o
 obj-$(CONFIG_MCP320X) += mcp320x.o
 obj-$(CONFIG_MCP3422) += mcp3422.o
+obj-$(CONFIG_MCP3564) += mcp3564.o
 obj-$(CONFIG_MCP3911) += mcp3911.o
 obj-$(CONFIG_MEDIATEK_MT6360_ADC) += mt6360-adc.o
 obj-$(CONFIG_MEDIATEK_MT6370_ADC) += mt6370-adc.o