[PATCH 3/3] iio: Documentation: Add initial documentaton for IIO

[Daniel Baluta <daniel.baluta@intel.com>]

This file wants to be a starting point document for anyone wanting
to use IIO configfs support or adding new IIO configfs functionality.

Signed-off-by: Daniel Baluta <daniel.baluta@intel.com>
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 Documentation/iio/iio_configfs.txt | 74 ++++++++++++++++++++++++++++++++++++++
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 create mode 100644 Documentation/iio/iio_configfs.txt

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+Industrial IIO configfs support
+
+1. Overview
+
+Configfs is a filesystem-based manager of kernel objects. IIO uses some
+objects that could be easily configured using configfs (e.g: devices,
+triggers).
+
+See Documentation/filesystems/configfs/configfs.txt for more information about
+how configfs works.
+
+2. Usage
+
+In order to use configfs support in IIO we need to select it at compile time
+via CONFIG_IIO_CONFIGFS config option.
+
+Then, mount the configfs filesystem (usually under /config directory):
+
+$ mkdir /config
+$ mount -t configfs none /config
+
+At this point, all default IIO groups will be creatd and can be accessed under
+/config/iio. Next chapters will describe available IIO configurable objects.
+
+2.1. Software triggers creation and destruction
+
+One of the IIO default configfs groups is the "triggers" groups. It is
+automagically accessible when the configfs is mounted and can be found under
+/config/iio/triggers.
+
+2.1.1. Trigger creation
+
+As simply as:
+
+$ mkdir /config/triggers/my_trigger
+
+This will create a directory associated with a trigger. To understand how this
+works we first need to see "my_triggers"'s attributes:
+
+$ ls /config/triggers/my_trigger
+activate            sampling_frequency  type
+
+Available types for triggers are:
+	* none, this is a default dummy trigger that does nothing.
+	* hrtimer, this is trigger based on high resolution timer.
+
+Order of operations in order to create a "hrtimer" trigger:
+
+$ echo hrtimer > /config/triggers/my_trigger/type
+$ echo 1 > /config/triggers/my_trigger/activate
+$ echo 100 > /config/triggers/my_trigger/sampling_frequency
+
+At this point the trigger can be used by an IIO device.
+
+2.1.2 Trigger destruction
+
+$ echo 1 > /config/triggers/my_trigger/activate
+
+3. Misc
+
+In order to add a new trigger type, one need to implement a driver that creates
+an instance of struct iio_configfs_ops (see iio_configfs_trigger.h header file
+in include/linux/iio) and then support it in iio_trigger_set_configfs_ops
+function from industrialiio-configfs.c file.
+
+These are the existing drivers implementing new trigger types:
+	* hrtimer => iio/trigger/iio-trig-hrtimer.c
+
+4. Further work
+
+* IIO dummy device creation
+* Mappings to 'soft' in kernel users such as iio_input and iio_hwmon
+* IIO on IIO drivers
+
-- 
1.9.1