===============================

  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" group. It is
  automagically accessible when the configfs is mounted and can be found
  under /config/iio/triggers.
  
  IIO software triggers implementation offers support for creating multiple
  trigger types. A new trigger type is usually implemented as a separate

  kernel module following the interface in include/linux/iio/sw_trigger.h::

    /*
     * drivers/iio/trigger/iio-trig-sample.c
     * sample kernel module implementing a new trigger type
     */
    #include <linux/iio/sw_trigger.h>

    static struct iio_sw_trigger *iio_trig_sample_probe(const char *name)
    {

  	/*
  	 * This allocates and registers an IIO trigger plus other
  	 * trigger type specific initialization.
  	 */

    }

    static int iio_trig_hrtimer_remove(struct iio_sw_trigger *swt)
    {

  	/*
  	 * This undoes the actions in iio_trig_sample_probe
  	 */

    }

    static const struct iio_sw_trigger_ops iio_trig_sample_ops = {

  	.probe		= iio_trig_sample_probe,
  	.remove		= iio_trig_sample_remove,

    };

    static struct iio_sw_trigger_type iio_trig_sample = {

  	.name = "trig-sample",
  	.owner = THIS_MODULE,
  	.ops = &iio_trig_sample_ops,

    };

  
  module_iio_sw_trigger_driver(iio_trig_sample);
  
  Each trigger type has its own directory under /config/iio/triggers. Loading
  iio-trig-sample module will create 'trig-sample' trigger type directory
  /config/iio/triggers/trig-sample.
  
  We support the following interrupt sources (trigger types):

  	* hrtimer, uses high resolution timers as interrupt source
  
  3.1 Hrtimer triggers creation and destruction

  ---------------------------------------------

  
  Loading iio-trig-hrtimer module will register hrtimer trigger types allowing
  users to create hrtimer triggers under /config/iio/triggers/hrtimer.

  e.g::

    $ mkdir /config/iio/triggers/hrtimer/instance1
    $ rmdir /config/iio/triggers/hrtimer/instance1

  
  Each trigger can have one or more attributes specific to the trigger type.
  
  3.2 "hrtimer" trigger types attributes

  --------------------------------------

  
  "hrtimer" trigger type doesn't have any configurable attribute from /config dir.
  It does introduce the sampling_frequency attribute to trigger directory.