iio: pulse: Support PWM capture with TI AM3358 eCAP module

This IIO driver adds support for PWM capture with the TI eCAP module.
This driver is based on Matt Porter's eCAP driver from January 2014,
which was never merged into the mainline [1]. Like Matt's code, this
driver implements interrupt driven triggered buffer capture. However,
the driver has been updated based on previous suggestions in the IIO
mailing list. Additionally, support for prescalar control and finer
polarity control has been included. Users can now configure the
polarities of CAP1 and CAP2 individually, allowing for the measurement
of a signal's high-time, low-time, or period.

[1] https://marc.info/?l=linux-iio&m=145968010427392&w=2

Signed-off-by: Darren Schachter <dts86@cornell.edu>

drivers/iio/Kconfig

@@ -93,6 +93,7 @@ source "drivers/iio/potentiometer/Kconfig"
 source "drivers/iio/potentiostat/Kconfig"
 source "drivers/iio/pressure/Kconfig"
 source "drivers/iio/proximity/Kconfig"
+source "drivers/iio/pulse/Kconfig"
 source "drivers/iio/resolver/Kconfig"
 source "drivers/iio/temperature/Kconfig"
 

drivers/iio/Makefile

@@ -36,6 +36,7 @@ obj-y += potentiometer/
 obj-y += potentiostat/
 obj-y += pressure/
 obj-y += proximity/
+obj-y += pulse/
 obj-y += resolver/
 obj-y += temperature/
 obj-y += trigger/

drivers/iio/industrialio-core.c

@@ -87,6 +87,7 @@ static const char * const iio_chan_type_name_spec[] = {
 	[IIO_POSITIONRELATIVE]  = "positionrelative",
 	[IIO_PHASE] = "phase",
 	[IIO_MASSCONCENTRATION] = "massconcentration",
+	[IIO_PULSE] = "pulse",
 };
 
 static const char * const iio_modifier_names[] = {

drivers/iio/pulse/Kconfig

@@ -0,0 +1,18 @@
+#
+# Pulse Capture Devices
+#
+# When adding new entries keep the list in alphabetical order
+
+menu "Pulse Capture Devices"
+
+config IIO_TIECAP
+	tristate "TI ECAP Pulse Capture"
+	depends on ARCH_OMAP2PLUS || ARCH_DAVINCI_DA8XX || ARCH_KEYSTONE || ARCH_K3 || COMPILE_TEST
+	select IIO_BUFFER
+	select IIO_TRIGGERED_BUFFER
+	help
+	  If you say yes here you get support for the TI ECAP peripheral
+	  in pulse capture mode. This driver can also be built as a
+	  module. If so, the module will be called pulse_tiecap.
+
+endmenu

drivers/iio/pulse/Makefile

@@ -0,0 +1,6 @@
+#
+# Makefile for IIO PWM Capture Device
+#
+
+# When adding new entries keep the list in alphabetical order
+obj-$(CONFIG_IIO_TIECAP)	+= pulse_tiecap.o