iio: afe: rescale: new driver

If an ADC channel measures the midpoint of a voltage divider, the
interesting voltage is often the voltage over the full resistance.
E.g. if the full voltage is too big for the ADC to handle.
Likewise, if an ADC channel measures the voltage across a shunt
resistor, with or without amplification, the interesting value is
often the current through the resistor.

This driver solves these problems by allowing to linearly scale a channel
and/or by allowing changes to the type of the channel.

Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

MAINTAINERS

@@ -6905,6 +6905,7 @@ S:	Maintained
 F:	Documentation/devicetree/bindings/iio/afe/current-sense-amplifier.txt
 F:	Documentation/devicetree/bindings/iio/afe/current-sense-shunt.txt
 F:	Documentation/devicetree/bindings/iio/afe/voltage-divider.txt
+F:	drivers/iio/afe/iio-rescale.c
 
 IKANOS/ADI EAGLE ADSL USB DRIVER
 M:	Matthieu Castet <castet.matthieu@free.fr>

drivers/iio/Kconfig

@@ -70,6 +70,7 @@ config IIO_TRIGGERED_EVENT
 
 source "drivers/iio/accel/Kconfig"
 source "drivers/iio/adc/Kconfig"
+source "drivers/iio/afe/Kconfig"
 source "drivers/iio/amplifiers/Kconfig"
 source "drivers/iio/chemical/Kconfig"
 source "drivers/iio/common/Kconfig"

drivers/iio/Makefile

@@ -15,6 +15,7 @@ obj-$(CONFIG_IIO_TRIGGERED_EVENT) += industrialio-triggered-event.o
 
 obj-y += accel/
 obj-y += adc/
+obj-y += afe/
 obj-y += amplifiers/
 obj-y += buffer/
 obj-y += chemical/

drivers/iio/afe/Kconfig

@@ -0,0 +1,19 @@
+#
+# Analog Front End drivers
+#
+# When adding new entries keep the list in alphabetical order
+
+menu "Analog Front Ends"
+
+config IIO_RESCALE
+	tristate "IIO rescale"
+	depends on OF || COMPILE_TEST
+	help
+	  Say yes here to build support for the IIO rescaling
+	  that handles voltage dividers, current sense shunts and
+	  current sense amplifiers.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called iio-rescale.
+
+endmenu

drivers/iio/afe/Makefile

@@ -0,0 +1,6 @@
+#
+# Makefile for industrial I/O Analog Front Ends (AFE)
+#
+
+# When adding new entries keep the list in alphabetical order
+obj-$(CONFIG_IIO_RESCALE) += iio-rescale.o