1========
2Triggers
3========
4
5* struct :c:type:`iio_trigger` — industrial I/O trigger device
6* :c:func:`devm_iio_trigger_alloc` — Resource-managed iio_trigger_alloc
7* :c:func:`devm_iio_trigger_register` — Resource-managed iio_trigger_register
8  iio_trigger_unregister
9* :c:func:`iio_trigger_validate_own_device` — Check if a trigger and IIO
10  device belong to the same device
11
12In many situations it is useful for a driver to be able to capture data based
13on some external event (trigger) as opposed to periodically polling for data.
14An IIO trigger can be provided by a device driver that also has an IIO device
15based on hardware generated events (e.g. data ready or threshold exceeded) or
16provided by a separate driver from an independent interrupt source (e.g. GPIO
17line connected to some external system, timer interrupt or user space writing
18a specific file in sysfs). A trigger may initiate data capture for a number of
19sensors and also it may be completely unrelated to the sensor itself.
20
21IIO trigger sysfs interface
22===========================
23
24There are two locations in sysfs related to triggers:
25
26* :file:`/sys/bus/iio/devices/trigger{Y}/*`, this file is created once an
27  IIO trigger is registered with the IIO core and corresponds to trigger
28  with index Y.
29  Because triggers can be very different depending on type there are few
30  standard attributes that we can describe here:
31
32  * :file:`name`, trigger name that can be later used for association with a
33    device.
34  * :file:`sampling_frequency`, some timer based triggers use this attribute to
35    specify the frequency for trigger calls.
36
37* :file:`/sys/bus/iio/devices/iio:device{X}/trigger/*`, this directory is
38  created once the device supports a triggered buffer. We can associate a
39  trigger with our device by writing the trigger's name in the
40  :file:`current_trigger` file.
41
42IIO trigger setup
43=================
44
45Let's see a simple example of how to setup a trigger to be used by a driver::
46
47      struct iio_trigger_ops trigger_ops = {
48          .set_trigger_state = sample_trigger_state,
49          .validate_device = sample_validate_device,
50      }
51
52      struct iio_trigger *trig;
53
54      /* first, allocate memory for our trigger */
55      trig = iio_trigger_alloc(dev, "trig-%s-%d", name, idx);
56
57      /* setup trigger operations field */
58      trig->ops = &trigger_ops;
59
60      /* now register the trigger with the IIO core */
61      iio_trigger_register(trig);
62
63IIO trigger ops
64===============
65
66* struct :c:type:`iio_trigger_ops` — operations structure for an iio_trigger.
67
68Notice that a trigger has a set of operations attached:
69
70* :file:`set_trigger_state`, switch the trigger on/off on demand.
71* :file:`validate_device`, function to validate the device when the current
72  trigger gets changed.
73
74More details
75============
76.. kernel-doc:: include/linux/iio/trigger.h
77.. kernel-doc:: drivers/iio/industrialio-trigger.c
78   :export:
79