iio: health: Add driver for the TI AFE4404 heart monitor

Add driver for the TI AFE4404 heart rate monitor and pulse oximeter.
This device detects reflected LED light fluctuations and presents an ADC
value to the user space for further signal processing.

Datasheet: http://www.ti.com/product/AFE4404/datasheet

Signed-off-by: Andrew F. Davis <afd@ti.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/ABI/testing/sysfs-bus-iio-health-afe440x

@@ -0,0 +1,54 @@
+What:		/sys/bus/iio/devices/iio:deviceX/tia_resistanceY
+		/sys/bus/iio/devices/iio:deviceX/tia_capacitanceY
+Date:		December 2015
+KernelVersion:
+Contact:	Andrew F. Davis <afd@ti.com>
+Description:
+		Get and set the resistance and the capacitance settings for the
+		Transimpedance Amplifier. Y is 1 for Rf1 and Cf1, Y is 2 for
+		Rf2 and Cf2 values.
+
+What:		/sys/bus/iio/devices/iio:deviceX/tia_separate_en
+Date:		December 2015
+KernelVersion:
+Contact:	Andrew F. Davis <afd@ti.com>
+Description:
+		Enable or disable separate settings for the TransImpedance
+		Amplifier above, when disabled both values are set by the
+		first channel.
+
+What:		/sys/bus/iio/devices/iio:deviceX/in_intensity_ledY_raw
+		/sys/bus/iio/devices/iio:deviceX/in_intensity_ledY_ambient_raw
+Date:		December 2015
+KernelVersion:
+Contact:	Andrew F. Davis <afd@ti.com>
+Description:
+		Get measured values from the ADC for these stages. Y is the
+		specific LED number. The values are expressed in 24-bit twos
+		complement.
+
+What:		/sys/bus/iio/devices/iio:deviceX/in_intensity_ledY-ledY_ambient_raw
+Date:		December 2015
+KernelVersion:
+Contact:	Andrew F. Davis <afd@ti.com>
+Description:
+		Get differential values from the ADC for these stages. Y is the
+		specific LED number. The values are expressed in 24-bit twos
+		complement for the specified LEDs.
+
+What:		/sys/bus/iio/devices/iio:deviceX/out_current_ledY_offset
+		/sys/bus/iio/devices/iio:deviceX/out_current_ledY_ambient_offset
+Date:		December 2015
+KernelVersion:
+Contact:	Andrew F. Davis <afd@ti.com>
+Description:
+		Get and set the offset cancellation DAC setting for these
+		stages. The values are expressed in 5-bit sign-magnitude.
+
+What:		/sys/bus/iio/devices/iio:deviceX/out_current_ledY_raw
+Date:		December 2015
+KernelVersion:
+Contact:	Andrew F. Davis <afd@ti.com>
+Description:
+		Get and set the LED current for the specified LED. Y is the
+		specific LED number.

drivers/iio/health/Kconfig

@@ -3,7 +3,22 @@
 #
 # When adding new entries keep the list in alphabetical order
 
-menu "Health sensors"
+menu "Health Sensors"
+
+menu "Heart Rate Monitors"
+
+config AFE4404
+	tristate "TI AFE4404 heart rate and pulse oximeter sensor"
+	depends on I2C
+	select REGMAP_I2C
+	select IIO_BUFFER
+	select IIO_TRIGGERED_BUFFER
+	help
+	  Say yes to choose the Texas Instruments AFE4404
+	  heart rate monitor and low-cost pulse oximeter.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called afe4404.
 
 config MAX30100
 	tristate "MAX30100 heart rate and pulse oximeter sensor"
@@ -19,3 +34,5 @@ config MAX30100
 	  module will be called max30100.
 
 endmenu
+
+endmenu

drivers/iio/health/Makefile

@@ -4,4 +4,5 @@
 
 # When adding new entries keep the list in alphabetical order
 
+obj-$(CONFIG_AFE4404)		+= afe4404.o
 obj-$(CONFIG_MAX30100)		+= max30100.o