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