IIO Device drivers
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This is not intended to provide a comprehensive guide to writing an
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IIO device driver. For further information see the drivers within the
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subsystem.
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The crucial structure for device drivers in iio is iio_dev.
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First allocate one using:
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struct iio_dev *indio_dev = iio_device_alloc(sizeof(struct chip_state));
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where chip_state is a structure of local state data for this instance of
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the chip.
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That data can be accessed using iio_priv(struct iio_dev *).
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Then fill in the following:
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- indio_dev->dev.parent
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Struct device associated with the underlying hardware.
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- indio_dev->name
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Name of the device being driven - made available as the name
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attribute in sysfs.
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- indio_dev->info
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pointer to a structure with elements that tend to be fixed for
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large sets of different parts supported by a given driver.
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This contains:
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* info->event_attrs:
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Attributes used to enable / disable hardware events.
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* info->attrs:
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General device attributes. Typically used for the weird
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and the wonderful bits not covered by the channel specification.
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* info->read_raw:
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Raw data reading function. Used for both raw channel access
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and for associate parameters such as offsets and scales.
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* info->write_raw:
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Raw value writing function. Used for writable device values such
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as DAC values and calibbias.
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* info->read_event_config:
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Typically only set if there are some interrupt lines. This
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is used to read if an on sensor event detector is enabled.
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* info->write_event_config:
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Enable / disable an on sensor event detector.
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* info->read_event_value:
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Read value associated with on sensor event detectors. Note that
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the meaning of the returned value is dependent on the event
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type.
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* info->write_event_value:
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Write the value associated with on sensor event detectors. E.g.
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a threshold above which an interrupt occurs. Note that the
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meaning of the value to be set is event type dependent.
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- indio_dev->modes:
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Specify whether direct access and / or ring buffer access is supported.
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- indio_dev->buffer:
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An optional associated buffer.
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- indio_dev->pollfunc:
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Poll function related elements. This controls what occurs when a trigger
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to which this device is attached sends an event.
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- indio_dev->channels:
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Specification of device channels. Most attributes etc. are built
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from this spec.
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- indio_dev->num_channels:
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How many channels are there?
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Once these are set up, a call to iio_device_register(indio_dev)
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will register the device with the iio core.
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Worth noting here is that, if a ring buffer is to be used, it can be
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allocated prior to registering the device with the iio-core, but must
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be registered afterwards (otherwise the whole parentage of devices
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gets confused)
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On remove, iio_device_unregister(indio_dev) will remove the device from
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the core, and iio_device_free(indio_dev) will clean up.
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