[PATCH v2 3/3] iio: Documentation: Add documentation for IIO configfs

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

Signed-off-by: Daniel Baluta <daniel.baluta@intel.com>
---
Changes since v1:
	* addressed feedback for v1:
		* https://lkml.org/lkml/2015/3/25/648
	* adapted to match the changes in patches 1 and 2
	* fixed some typos and clarified further work

 Documentation/iio/iio_configfs.txt | 82 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 82 insertions(+)
 create mode 100644 Documentation/iio/iio_configfs.txt

diff --git a/Documentation/iio/iio_configfs.txt b/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 created and can be accessed
+under /config/iio. Next chapters will describe available IIO configuration
+objects.
+
+3. Software triggers
+
+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.
+
+Under /config/iio/triggers we will create trigger types. For the moment
+we have "hrtimer" trigger time and we plan to add at least one more
+"sysfs" trigger type.
+
+3.1 Trigger types
+
+Represent a specific type of trigger. For now we have an implementation
+for "hrtimer" trigger type.
+
+3.2. Trigger creation and destruction
+
+As simply as:
+
+$ mkdir /config/triggers/hrtimer/my_trigger
+
+Creating my_trigger directory will result in creation of "my_trigger"
+trigger of "hrtimer" type.  Destruction happens when my_trigger directory
+is removed.
+
+Each trigger can have one or more attributes specific to the trigger type.
+
+3.3 "hrtimer" trigger types attributes
+
+"hrtimer" trigger type has only one attribute:
+
+$ ls /config/triggers/hrtimer/my_trigger delay
+
+delay - represents the amount of time in nanoseconds between two
+consecutive iio_trigger_poll calls. By default it is set to 100000000,
+that is the equivalent of a 100Hz frequency.
+
+3.4. Adding a new trigger type
+
+In order to add a new trigger type, one needs to:
+
+* [iio_configfs_trigger.h]
+	** add a new IIO_TRIGGER_TYPE
+* [iio-trig-<type>.c]
+	** declare and initialize a structure of type
+	iio_configfs_trigger_type
+	** implement needed iio_configfs_trigger_ops
+	** register/unregister the new trigger
+	type with the IIO configfs core
+* [industrialiio-configfs.c]
+	** create a new group type and add it in the default group of
+	   trigger types.
+	** create new attributes and them to the IIO configfs core.
+
+4. Further work
+
+* add "sysfs" trigger type
+
-- 
1.9.1