iio: cros_ec_sensors_core: Add common functions for the ChromeOS EC Sensor Hub.

Add the core functions to be able to support the sensors attached behind
the ChromeOS Embedded Controller and used by other IIO cros-ec sensor
drivers.

The cros_ec_sensor_core driver matches with current driver in ChromeOS
4.4 tree, so it includes all the fixes at the moment. The support for
this driver was made by Gwendal Grignou. The original patch and all the
fixes has been squashed and rebased on top of mainline.

Signed-off-by: Gwendal Grignou <[email protected]>
Signed-off-by: Guenter Roeck <[email protected]>
[eballetbo: split, squash and rebase on top of mainline the patches
found in ChromeOS tree]
Signed-off-by: Enric Balletbo i Serra <[email protected]>
Signed-off-by: Jonathan Cameron <[email protected]>

Author: Enric Balletbo i Serra

Documentation/ABI/testing/sysfs-bus-iio-cros-ec

@@ -0,0 +1,18 @@
+What:		/sys/bus/iio/devices/iio:deviceX/calibrate
+Date:		July 2015
+KernelVersion:	4.7
+Contact:	[email protected]
+Description:
+		Writing '1' will perform a FOC (Fast Online Calibration). The
+                corresponding calibration offsets can be read from *_calibbias
+                entries.
+
+What:		/sys/bus/iio/devices/iio:deviceX/location
+Date:		July 2015
+KernelVersion:	4.7
+Contact:	[email protected]
+Description:
+		This attribute returns a string with the physical location where
+                the motion sensor is placed. For example, in a laptop a motion
+                sensor can be located on the base or on the lid. Current valid
+		values are 'base' and 'lid'.

drivers/iio/common/Kconfig

@@ -2,6 +2,7 @@
 # IIO common modules
 #
 
+source "drivers/iio/common/cros_ec_sensors/Kconfig"
 source "drivers/iio/common/hid-sensors/Kconfig"
 source "drivers/iio/common/ms_sensors/Kconfig"
 source "drivers/iio/common/ssp_sensors/Kconfig"

drivers/iio/common/Makefile

@@ -7,6 +7,7 @@
 #
 
 # When adding new entries keep the list in alphabetical order
+obj-y += cros_ec_sensors/
 obj-y += hid-sensors/
 obj-y += ms_sensors/
 obj-y += ssp_sensors/

drivers/iio/common/cros_ec_sensors/Kconfig

@@ -0,0 +1,14 @@
+#
+# Chrome OS Embedded Controller managed sensors library
+#
+config IIO_CROS_EC_SENSORS_CORE
+	tristate "ChromeOS EC Sensors Core"
+	depends on SYSFS && MFD_CROS_EC
+	select IIO_BUFFER
+	select IIO_TRIGGERED_BUFFER
+	help
+	  Base module for the ChromeOS EC Sensors module.
+	  Contains core functions used by other IIO CrosEC sensor
+	  drivers.
+	  Define common attributes and sysfs interrupt handler.
+

drivers/iio/common/cros_ec_sensors/Makefile

@@ -0,0 +1,5 @@
+#
+# Makefile for sensors seen through the ChromeOS EC sensor hub.
+#
+
+obj-$(CONFIG_IIO_CROS_EC_SENSORS_CORE) += cros_ec_sensors_core.o