iio: adc: add support for pac1921

Add support for Microchip PAC1921 Power/Current monitor.

Implemented features:
* capture of bus voltage, sense voltage, current and power measurements
  in free-run integration mode
* support for both raw and triggered buffer reading
* support for overflow events
* scale attributes to control voltage and current gains
* oversampling ratio attribute to control the number of integration
  samples
* sampling rate attribute that reflects the integration period
* userspace attribute and DT parameter to control shunt resistor
* simple power management support

Limitations:
* operation mode fixed to free-run integration
* READ/INT pin and OUT pin not supported
* no controls for measurement resolutions and filters

Signed-off-by: Matteo Martelli <matteomartelli3@gmail.com>
Link: https://patch.msgid.link/20240724-iio-pac1921-v4-3-723698e903a3@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Author: mattmart3

MAINTAINERS

@@ -15054,6 +15054,13 @@ F:	Documentation/devicetree/bindings/nvmem/microchip,sama7g5-otpc.yaml
 F:	drivers/nvmem/microchip-otpc.c
 F:	include/dt-bindings/nvmem/microchip,sama7g5-otpc.h
 
+MICROCHIP PAC1921 POWER/CURRENT MONITOR DRIVER
+M:	Matteo Martelli <matteomartelli3@gmail.com>
+L:	linux-iio@vger.kernel.org
+S:	Supported
+F:	Documentation/devicetree/bindings/iio/adc/microchip,pac1921.yaml
+F:	drivers/iio/adc/pac1921.c
+
 MICROCHIP PAC1934 POWER/ENERGY MONITOR DRIVER
 M:	Marius Cristea <marius.cristea@microchip.com>
 L:	linux-iio@vger.kernel.org

drivers/iio/adc/Kconfig

@@ -1002,6 +1002,19 @@ config NPCM_ADC
 	  This driver can also be built as a module. If so, the module
 	  will be called npcm_adc.
 
+config PAC1921
+	tristate "Microchip Technology PAC1921 driver"
+	depends on I2C
+	select REGMAP_I2C
+	select IIO_BUFFER
+	select IIO_TRIGGERED_BUFFER
+	help
+	  Say yes here to build support for Microchip Technology's PAC1921
+	  High-Side Power/Current Monitor with Analog Output.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called pac1921.
+
 config PAC1934
 	tristate "Microchip Technology PAC1934 driver"
 	depends on I2C

drivers/iio/adc/Makefile

@@ -91,6 +91,7 @@ obj-$(CONFIG_MP2629_ADC) += mp2629_adc.o
 obj-$(CONFIG_MXS_LRADC_ADC) += mxs-lradc-adc.o
 obj-$(CONFIG_NAU7802) += nau7802.o
 obj-$(CONFIG_NPCM_ADC) += npcm_adc.o
+obj-$(CONFIG_PAC1921) += pac1921.o
 obj-$(CONFIG_PAC1934) += pac1934.o
 obj-$(CONFIG_PALMAS_GPADC) += palmas_gpadc.o
 obj-$(CONFIG_QCOM_PM8XXX_XOADC) += qcom-pm8xxx-xoadc.o