LXR linux/drivers/staging/iio/Documentation/device.txt

   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->ring:
  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