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Industrial I/O Subsystem in kernel consumers.
The IIO subsystem can act as a layer under other elements of the kernel
providing a means of obtaining ADC type readings or of driving DAC type
signals. The functionality supported will grow as use cases arise.
Describing the channel mapping (iio/machine.h)
Channel associations are described using:
struct iio_map {
const char *adc_channel_label;
const char *consumer_dev_name;
const char *consumer_channel;
adc_channel_label identifies the channel on the IIO device by being
matched against the datasheet_name field of the iio_chan_spec.
consumer_dev_name allows identification of the consumer device.
This are then used to find the channel mapping from the consumer device (see
Finally consumer_channel is a string identifying the channel to the consumer.
(Perhaps 'battery_voltage' or similar).
An array of these structures is then passed to the IIO driver.
Supporting in kernel interfaces in the driver (driver.h)
The driver must provide datasheet_name values for its channels and
must pass the iio_map structures and a pointer to its own iio_dev structure
on to the core via a call to iio_map_array_register. On removal,
iio_map_array_unregister reverses this process.
The result of this is that the IIO core now has all the information needed
to associate a given channel with the consumer requesting it.
Acting as an IIO consumer (consumer.h)
The consumer first has to obtain an iio_channel structure from the core
by calling iio_channel_get(). The correct channel is identified by:
* matching dev or dev_name against consumer_dev and consumer_dev_name
* matching consumer_channel against consumer_channel in the map
There are then a number of functions that can be used to get information
about this channel such as it's current reading.
iio_read_channel_raw() - get a reading
iio_get_channel_type() - get the type of channel
There is also provision for retrieving all of the channels associated
with a given consumer. This is useful for generic drivers such as
iio_hwmon where the number and naming of channels is not known by the
consumer driver. To do this, use iio_channel_get_all.