iio_configfs.rst

  1===============================
  2Industrial IIO configfs support
  3===============================
  4
  51. Overview
  6===========
  7
  8Configfs is a filesystem-based manager of kernel objects. IIO uses some
  9objects that could be easily configured using configfs (e.g.: devices,
 10triggers).
 11
 12See Documentation/filesystems/configfs.rst for more information
 13about how configfs works.
 14
 152. Usage
 16========
 17
 18In order to use configfs support in IIO we need to select it at compile
 19time via CONFIG_IIO_CONFIGFS config option.
 20
 21Then, mount the configfs filesystem (usually under /config directory)::
 22
 23  $ mkdir /config
 24  $ mount -t configfs none /config
 25
 26At this point, all default IIO groups will be created and can be accessed
 27under /config/iio. Next chapters will describe available IIO configuration
 28objects.
 29
 303. Software triggers
 31====================
 32
 33One of the IIO default configfs groups is the "triggers" group. It is
 34automagically accessible when the configfs is mounted and can be found
 35under /config/iio/triggers.
 36
 37IIO software triggers implementation offers support for creating multiple
 38trigger types. A new trigger type is usually implemented as a separate
 39kernel module following the interface in include/linux/iio/sw_trigger.h::
 40
 41  /*
 42   * drivers/iio/trigger/iio-trig-sample.c
 43   * sample kernel module implementing a new trigger type
 44   */
 45  #include <linux/iio/sw_trigger.h>
 46
 47
 48  static struct iio_sw_trigger *iio_trig_sample_probe(const char *name)
 49  {
 50	/*
 51	 * This allocates and registers an IIO trigger plus other
 52	 * trigger type specific initialization.
 53	 */
 54  }
 55
 56  static int iio_trig_sample_remove(struct iio_sw_trigger *swt)
 57  {
 58	/*
 59	 * This undoes the actions in iio_trig_sample_probe
 60	 */
 61  }
 62
 63  static const struct iio_sw_trigger_ops iio_trig_sample_ops = {
 64	.probe		= iio_trig_sample_probe,
 65	.remove		= iio_trig_sample_remove,
 66  };
 67
 68  static struct iio_sw_trigger_type iio_trig_sample = {
 69	.name = "trig-sample",
 70	.owner = THIS_MODULE,
 71	.ops = &iio_trig_sample_ops,
 72  };
 73
 74  module_iio_sw_trigger_driver(iio_trig_sample);
 75
 76Each trigger type has its own directory under /config/iio/triggers. Loading
 77iio-trig-sample module will create 'trig-sample' trigger type directory
 78/config/iio/triggers/trig-sample.
 79
 80We support the following interrupt sources (trigger types):
 81
 82	* hrtimer, uses high resolution timers as interrupt source
 83
 843.1 Hrtimer triggers creation and destruction
 85---------------------------------------------
 86
 87Loading iio-trig-hrtimer module will register hrtimer trigger types allowing
 88users to create hrtimer triggers under /config/iio/triggers/hrtimer.
 89
 90e.g::
 91
 92  $ mkdir /config/iio/triggers/hrtimer/instance1
 93  $ rmdir /config/iio/triggers/hrtimer/instance1
 94
 95Each trigger can have one or more attributes specific to the trigger type.
 96
 973.2 "hrtimer" trigger types attributes
 98--------------------------------------
 99
100"hrtimer" trigger type doesn't have any configurable attribute from /config dir.
101It does introduce the sampling_frequency attribute to trigger directory.
102That attribute sets the polling frequency in Hz, with mHz precision.