iio: Add SEMTECH SX9310/9311 sensor driver

Add SEMTECH SX9310/9311 driver.

The device has the following entry points:

Usual frequency:
- sampling_frequency
- sampling_frequency_available

Instant reading of current values for different sensors:
- in_proximity0_raw
- in_proximity1_raw
- in_proximity2_raw
- in_proximity3_comb_raw
and associated events in events/
Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Signed-off-by: Enrico Granata <egranata@chromium.org>
Signed-off-by: Daniel Campello <campello@chromium.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/ABI/testing/sysfs-bus-iio-sx9310

+What:		/sys/bus/iio/devices/iio:deviceX/in_proximity3_comb_raw
+Date:		February 2019
+KernelVersion:	5.6
+Contact:	Daniel Campello <campello@chromium.org>
+Description:
+		Proximity measurement indicating that some object is
+		near the combined sensor. The combined sensor presents
+		proximity measurements constructed by hardware by
+		combining measurements taken from a given set of
+		physical sensors.

drivers/iio/proximity/Kconfig

@@ -101,6 +101,19 @@ config SRF04
 	  To compile this driver as a module, choose M here: the
 	  module will be called srf04.
 
+config SX9310
+	tristate "SX9310/SX9311 Semtech proximity sensor"
+	select IIO_BUFFER
+	select IIO_TRIGGERED_BUFFER
+	select REGMAP_I2C
+	depends on I2C
+	help
+	  Say Y here to build a driver for Semtech's SX9310/SX9311 capacitive
+	  proximity/button sensor.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called sx9310.
+
 config SX9500
 	tristate "SX9500 Semtech proximity sensor"
 	select IIO_BUFFER

drivers/iio/proximity/Makefile

@@ -12,6 +12,7 @@ obj-$(CONFIG_PING)		+= ping.o
 obj-$(CONFIG_RFD77402)		+= rfd77402.o
 obj-$(CONFIG_SRF04)		+= srf04.o
 obj-$(CONFIG_SRF08)		+= srf08.o
+obj-$(CONFIG_SX9310)		+= sx9310.o
 obj-$(CONFIG_SX9500)		+= sx9500.o
 obj-$(CONFIG_VL53L0X_I2C)	+= vl53l0x-i2c.o