1IIO Device drivers
2
3This is not intended to provide a comprehensive guide to writing an
4IIO device driver.  For further information see the drivers within the
5subsystem.
6
7The crucial structure for device drivers in iio is iio_dev.
8
9First allocate one using:
10
11struct iio_dev *indio_dev = iio_device_alloc(sizeof(struct chip_state));
12where chip_state is a structure of local state data for this instance of
13the chip.
14
15That data can be accessed using iio_priv(struct iio_dev *).
16
17Then fill in the following:
18
19- indio_dev->dev.parent
20	Struct device associated with the underlying hardware.
21- indio_dev->name
22	Name of the device being driven - made available as the name
23	attribute in sysfs.
24
25- indio_dev->info
26	pointer to a structure with elements that tend to be fixed for
27	large sets of different parts supported by a given driver.
28	This contains:
29	* info->driver_module:
30		Set to THIS_MODULE. Used to ensure correct ownership
31		of various resources allocate by the core.
32	* info->event_attrs:
33		Attributes used to enable / disable hardware events.
34	* info->attrs:
35		General device attributes. Typically used for the weird
36		and the wonderful bits not covered by the channel specification.
37	* info->read_raw:
38		Raw data reading function. Used for both raw channel access
39		and for associate parameters such as offsets and scales.
40	* info->write_raw:
41		Raw value writing function. Used for writable device values such
42		as DAC values and calibbias.
43	* info->read_event_config:
44		Typically only set if there are some interrupt lines.  This
45		is used to read if an on sensor event detector is enabled.
46	* info->write_event_config:
47		Enable / disable an on sensor event detector.
48	* info->read_event_value:
49		Read value associated with on sensor event detectors. Note that
50		the meaning of the returned value is dependent on the event
51		type.
52	* info->write_event_value:
53		Write the value associated with on sensor event detectors. E.g.
54		a threshold above which an interrupt occurs.  Note that the
55		meaning of the value to be set is event type dependant.
56
57- indio_dev->modes:
58	Specify whether direct access and / or ring buffer access is supported.
59- indio_dev->buffer:
60	An optional associated buffer.
61- indio_dev->pollfunc:
62	Poll function related elements. This controls what occurs when a trigger
63	to which this device is attached sends an event.
64- indio_dev->channels:
65	Specification of device channels. Most attributes etc. are built
66	from this spec.
67- indio_dev->num_channels:
68	How many channels are there?
69
70Once these are set up, a call to iio_device_register(indio_dev)
71will register the device with the iio core.
72
73Worth noting here is that, if a ring buffer is to be used, it can be
74allocated prior to registering the device with the iio-core, but must
75be registered afterwards (otherwise the whole parentage of devices
76gets confused)
77
78On remove, iio_device_unregister(indio_dev) will remove the device from
79the core, and iio_device_free(indio_dev) will clean up.
80