iio:cdc:ad7150: Move driver out of staging.

This capacitance to digital converter (CDC) driver is compliant with
the IIO ABI.  Note, not all features supported (e.g. window event modes)
but the driver should be in a useful functional state.

The cleanup was done against QEMU emulation of the device rather than
actual hardware.   Whilst this was a bit of an experiment, it made it
easy to confirm that the driver remained in a consistent working state
through the various refactors.  If it worked in the first place, it
should still be working after this cleanup.

Given some IIO drivers require expensive hardware setups, (not particularly
true with this one) the use of QEMU may provide a viable way forward
for providing testing during code changes where previously we'd had
to rely on sharp eyes and crossed fingers.

Note, no explicit MAINTAINERS entry as it will be covered by the
generic catch-alls for ADI and IIO drivers which are sufficient.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20210314181511.531414-25-jic23@kernel.org

drivers/iio/Kconfig

@@ -72,6 +72,7 @@ source "drivers/iio/accel/Kconfig"
 source "drivers/iio/adc/Kconfig"
 source "drivers/iio/afe/Kconfig"
 source "drivers/iio/amplifiers/Kconfig"
+source "drivers/iio/cdc/Kconfig"
 source "drivers/iio/chemical/Kconfig"
 source "drivers/iio/common/Kconfig"
 source "drivers/iio/dac/Kconfig"

drivers/iio/Makefile

@@ -18,6 +18,7 @@ obj-y += adc/
 obj-y += afe/
 obj-y += amplifiers/
 obj-y += buffer/
+obj-y += cdc/
 obj-y += chemical/
 obj-y += common/
 obj-y += dac/

drivers/iio/cdc/Kconfig

@@ -0,0 +1,17 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# CDC drivers
+#
+menu "Capacitance to digital converters"
+
+config AD7150
+	tristate "Analog Devices ad7150/1/6 capacitive sensor driver"
+	depends on I2C
+	help
+	  Say yes here to build support for Analog Devices capacitive sensors.
+	  (ad7150, ad7151, ad7156) Provides direct access via sysfs.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called ad7150.
+
+endmenu

drivers/iio/cdc/Makefile

@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Makefile for industrial I/O capacitance to digital converter (CDC) drivers
+#
+
+obj-$(CONFIG_AD7150) += ad7150.o

drivers/staging/iio/cdc/Kconfig

@@ -4,16 +4,6 @@
 #
 menu "Capacitance to digital converters"
 
-config AD7150
-	tristate "Analog Devices ad7150/1/6 capacitive sensor driver"
-	depends on I2C
-	help
-	  Say yes here to build support for Analog Devices capacitive sensors.
-	  (ad7150, ad7151, ad7156) Provides direct access via sysfs.
-
-	  To compile this driver as a module, choose M here: the
-	  module will be called ad7150.
-
 config AD7746
 	tristate "Analog Devices AD7745, AD7746 AD7747 capacitive sensor driver"
 	depends on I2C

drivers/staging/iio/cdc/Makefile

@@ -1,7 +1,6 @@
 # SPDX-License-Identifier: GPL-2.0
 #
-# Makefile for industrial I/O DAC drivers
+# Makefile for industrial I/O CDC drivers
 #
 
-obj-$(CONFIG_AD7150) += ad7150.o
 obj-$(CONFIG_AD7746) += ad7746.o