Core elements¶

The Industrial I/O core offers both a unified framework for writing drivers for many different types of embedded sensors and a standard interface to user space applications manipulating sensors. The implementation can be found under drivers/iio/industrialio-*

Industrial I/O Devices¶

struct iio_dev - industrial I/O device
iio_device_alloc() - allocate an iio_dev from a driver
iio_device_free() - free an iio_dev from a driver
iio_device_register() - register a device with the IIO subsystem
iio_device_unregister() - unregister a device from the IIO subsystem

An IIO device usually corresponds to a single hardware sensor and it provides all the information needed by a driver handling a device. Let’s first have a look at the functionality embedded in an IIO device then we will show how a device driver makes use of an IIO device.

There are two ways for a user space application to interact with an IIO driver.

/sys/bus/iio/iio:deviceX/, this represents a hardware sensor and groups together the data channels of the same chip.
/dev/iio:deviceX, character device node interface used for buffered data transfer and for events information retrieval.

A typical IIO driver will register itself as an I2C or SPI driver and will create two routines, probe and remove.

At probe:

Call iio_device_alloc(), which allocates memory for an IIO device.
Initialize IIO device fields with driver specific information (e.g. device name, device channels).
Call iio_device_register(), this registers the device with the IIO core. After this call the device is ready to accept requests from user space applications.

At remove, we free the resources allocated in probe in reverse order:

iio_device_unregister(), unregister the device from the IIO core.
iio_device_free(), free the memory allocated for the IIO device.

IIO device sysfs interface¶

Attributes are sysfs files used to expose chip info and also allowing applications to set various configuration parameters. For device with index X, attributes can be found under /sys/bus/iio/iio:deviceX/ directory. Common attributes are:

name, description of the physical chip.
dev, shows the major:minor pair associated with /dev/iio:deviceX node.
sampling_frequency_available, available discrete set of sampling frequency values for device.
Available standard attributes for IIO devices are described in the Documentation/ABI/testing/sysfs-bus-iio file in the Linux kernel sources.

IIO device channels¶

struct iio_chan_spec - specification of a single channel

An IIO device channel is a representation of a data channel. An IIO device can have one or multiple channels. For example:

a thermometer sensor has one channel representing the temperature measurement.
a light sensor with two channels indicating the measurements in the visible and infrared spectrum.
an accelerometer can have up to 3 channels representing acceleration on X, Y and Z axes.

An IIO channel is described by the struct iio_chan_spec. A thermometer driver for the temperature sensor in the example above would have to describe its channel as follows:

static const struct iio_chan_spec temp_channel[] = {
     {
         .type = IIO_TEMP,
         .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED),
     },
};

Channel sysfs attributes exposed to userspace are specified in the form of bitmasks. Depending on their shared info, attributes can be set in one of the following masks:

info_mask_separate, attributes will be specific to this channel
info_mask_shared_by_type, attributes are shared by all channels of the same type
info_mask_shared_by_dir, attributes are shared by all channels of the same direction
info_mask_shared_by_all, attributes are shared by all channels

When there are multiple data channels per channel type we have two ways to distinguish between them:

set .modified field of iio_chan_spec to 1. Modifiers are specified using .channel2 field of the same iio_chan_spec structure and are used to indicate a physically unique characteristic of the channel such as its direction or spectral response. For example, a light sensor can have two channels, one for infrared light and one for both infrared and visible light.
set .indexed field of iio_chan_spec to 1. In this case the channel is simply another instance with an index specified by the .channel field.

Here is how we can make use of the channel’s modifiers:

static const struct iio_chan_spec light_channels[] = {
        {
                .type = IIO_INTENSITY,
                .modified = 1,
                .channel2 = IIO_MOD_LIGHT_IR,
                .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
                .info_mask_shared = BIT(IIO_CHAN_INFO_SAMP_FREQ),
        },
        {
                .type = IIO_INTENSITY,
                .modified = 1,
                .channel2 = IIO_MOD_LIGHT_BOTH,
                .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
                .info_mask_shared = BIT(IIO_CHAN_INFO_SAMP_FREQ),
        },
        {
                .type = IIO_LIGHT,
                .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED),
                .info_mask_shared = BIT(IIO_CHAN_INFO_SAMP_FREQ),
        },
   }

This channel’s definition will generate two separate sysfs files for raw data retrieval:

/sys/bus/iio/iio:deviceX/in_intensity_ir_raw
/sys/bus/iio/iio:deviceX/in_intensity_both_raw

one file for processed data:

/sys/bus/iio/iio:deviceX/in_illuminance_input

and one shared sysfs file for sampling frequency:

/sys/bus/iio/iio:deviceX/sampling_frequency.

Here is how we can make use of the channel’s indexing:

static const struct iio_chan_spec light_channels[] = {
        {
                .type = IIO_VOLTAGE,
                .indexed = 1,
                .channel = 0,
                .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
        },
        {
                .type = IIO_VOLTAGE,
                .indexed = 1,
                .channel = 1,
                .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
        },
}

This will generate two separate attributes files for raw data retrieval:

/sys/bus/iio/devices/iio:deviceX/in_voltage0_raw, representing voltage measurement for channel 0.
/sys/bus/iio/devices/iio:deviceX/in_voltage1_raw, representing voltage measurement for channel 1.

More details¶

struct iio_chan_spec_ext_info¶: Extended channel info attribute

Definition

struct iio_chan_spec_ext_info {
  const char *name;
  enum iio_shared_by shared;
  ssize_t (*read)(struct iio_dev *, uintptr_t private, struct iio_chan_spec const *, char *buf);
  ssize_t (*write)(struct iio_dev *, uintptr_t private,struct iio_chan_spec const *, const char *buf, size_t len);
  uintptr_t private;
};

Members

name: Info attribute name
shared: Whether this attribute is shared between all channels.
read: Read callback for this info attribute, may be NULL.
write: Write callback for this info attribute, may be NULL.
private: Data private to the driver.

struct iio_enum¶: Enum channel info attribute

Definition

struct iio_enum {
  const char * const *items;
  unsigned int num_items;
  int (*set)(struct iio_dev *, const struct iio_chan_spec *, unsigned int);
  int (*get)(struct iio_dev *, const struct iio_chan_spec *);
};

Members

items: An array of strings.
num_items: Length of the item array.
set: Set callback function, may be NULL.
get: Get callback function, may be NULL.

Description

The iio_enum struct can be used to implement enum style channel attributes. Enum style attributes are those which have a set of strings which map to unsigned integer values. The IIO enum helper code takes care of mapping between value and string as well as generating a “_available” file which contains a list of all available items. The set callback will be called when the attribute is updated. The last parameter is the index to the newly activated item. The get callback will be used to query the currently active item and is supposed to return the index for it.

IIO_ENUM¶

IIO_ENUM (_name, _shared, _e)

Initialize enum extended channel attribute

Parameters

_name: Attribute name
_shared: Whether the attribute is shared between all channels
_e: Pointer to an iio_enum struct

Description

This should usually be used together with IIO_ENUM_AVAILABLE()

IIO_ENUM_AVAILABLE¶

IIO_ENUM_AVAILABLE (_name, _e)

Initialize enum available extended channel attribute

Parameters

_name: Attribute name (“_available” will be appended to the name)
_e: Pointer to an iio_enum struct

Description

Creates a read only attribute which lists all the available enum items in a space separated list. This should usually be used together with IIO_ENUM()

struct iio_mount_matrix¶: iio mounting matrix

Definition

struct iio_mount_matrix {
  const char *rotation[9];
};

Members

rotation: 3 dimensional space rotation matrix defining sensor alignment with main hardware

IIO_MOUNT_MATRIX¶

IIO_MOUNT_MATRIX (_shared, _get)

Initialize mount matrix extended channel attribute

Parameters

_shared: Whether the attribute is shared between all channels
_get: Pointer to an iio_get_mount_matrix_t accessor

struct iio_event_spec¶: specification for a channel event

Definition

struct iio_event_spec {
  enum iio_event_type type;
  enum iio_event_direction dir;
  unsigned long mask_separate;
  unsigned long mask_shared_by_type;
  unsigned long mask_shared_by_dir;
  unsigned long mask_shared_by_all;
};

Members

type: Type of the event
dir: Direction of the event
mask_separate: Bit mask of enum iio_event_info values. Attributes set in this mask will be registered per channel.
mask_shared_by_type: Bit mask of enum iio_event_info values. Attributes set in this mask will be shared by channel type.
mask_shared_by_dir: Bit mask of enum iio_event_info values. Attributes set in this mask will be shared by channel type and direction.
mask_shared_by_all: Bit mask of enum iio_event_info values. Attributes set in this mask will be shared by all channels.

struct iio_chan_spec¶: specification of a single channel

Definition

struct iio_chan_spec {
  enum iio_chan_type      type;
  int channel;
  int channel2;
  unsigned long           address;
  int scan_index;
  struct {
    char sign;
    u8 realbits;
    u8 storagebits;
    u8 shift;
    u8 repeat;
    enum iio_endian endianness;
  } scan_type;
  long info_mask_separate;
  long info_mask_separate_available;
  long info_mask_shared_by_type;
  long info_mask_shared_by_type_available;
  long info_mask_shared_by_dir;
  long info_mask_shared_by_dir_available;
  long info_mask_shared_by_all;
  long info_mask_shared_by_all_available;
  const struct iio_event_spec *event_spec;
  unsigned int            num_event_specs;
  const struct iio_chan_spec_ext_info *ext_info;
  const char              *extend_name;
  const char              *datasheet_name;
  unsigned modified:1;
  unsigned indexed:1;
  unsigned output:1;
  unsigned differential:1;
};

Members

type: What type of measurement is the channel making.
channel: What number do we wish to assign the channel.
channel2: If there is a second number for a differential channel then this is it. If modified is set then the value here specifies the modifier.
address: Driver specific identifier.
scan_index: Monotonic index to give ordering in scans when read from a buffer.
scan_type: struct describing the scan type
scan_type.sign: ‘s’ or ‘u’ to specify signed or unsigned
scan_type.realbits: Number of valid bits of data
scan_type.storagebits: Realbits + padding
scan_type.shift: Shift right by this before masking out realbits.
scan_type.repeat: Number of times real/storage bits repeats. When the repeat element is more than 1, then the type element in sysfs will show a repeat value. Otherwise, the number of repetitions is omitted.
scan_type.endianness: little or big endian
info_mask_separate: What information is to be exported that is specific to this channel.
info_mask_separate_available: What availability information is to be exported that is specific to this channel.
info_mask_shared_by_type: What information is to be exported that is shared by all channels of the same type.
info_mask_shared_by_type_available: What availability information is to be exported that is shared by all channels of the same type.
info_mask_shared_by_dir: What information is to be exported that is shared by all channels of the same direction.
info_mask_shared_by_dir_available: What availability information is to be exported that is shared by all channels of the same direction.
info_mask_shared_by_all: What information is to be exported that is shared by all channels.
info_mask_shared_by_all_available: What availability information is to be exported that is shared by all channels.
event_spec: Array of events which should be registered for this channel.
num_event_specs: Size of the event_spec array.
ext_info: Array of extended info attributes for this channel. The array is NULL terminated, the last element should have its name field set to NULL.
extend_name: Allows labeling of channel attributes with an informative name. Note this has no effect codes etc, unlike modifiers.
datasheet_name: A name used in in-kernel mapping of channels. It should correspond to the first name that the channel is referred to by in the datasheet (e.g. IND), or the nearest possible compound name (e.g. IND-INC).
modified: Does a modifier apply to this channel. What these are depends on the channel type. Modifier is set in channel2. Examples are IIO_MOD_X for axial sensors about the ‘x’ axis.
indexed: Specify the channel has a numerical index. If not, the channel index number will be suppressed for sysfs attributes but not for event codes.
output: Channel is output.
differential: Channel is differential.

bool iio_channel_has_info(const struct iio_chan_spec *chan, enum iio_chan_info_enum type)¶: Checks whether a channel supports a info attribute

Parameters

const struct iio_chan_spec *chan: The channel to be queried
enum iio_chan_info_enum type: Type of the info attribute to be checked

Description

Returns true if the channels supports reporting values for the given info attribute type, false otherwise.

bool iio_channel_has_available(const struct iio_chan_spec *chan, enum iio_chan_info_enum type)¶: Checks if a channel has an available attribute

Parameters

const struct iio_chan_spec *chan: The channel to be queried
enum iio_chan_info_enum type: Type of the available attribute to be checked

Description

Returns true if the channel supports reporting available values for the given attribute type, false otherwise.

struct iio_info¶: constant information about device

Definition

struct iio_info {
  const struct attribute_group    *event_attrs;
  const struct attribute_group    *attrs;
  int (*read_raw)(struct iio_dev *indio_dev,struct iio_chan_spec const *chan,int *val,int *val2, long mask);
  int (*read_raw_multi)(struct iio_dev *indio_dev,struct iio_chan_spec const *chan,int max_len,int *vals,int *val_len, long mask);
  int (*read_avail)(struct iio_dev *indio_dev,struct iio_chan_spec const *chan,const int **vals,int *type,int *length, long mask);
  int (*write_raw)(struct iio_dev *indio_dev,struct iio_chan_spec const *chan,int val,int val2, long mask);
  int (*read_label)(struct iio_dev *indio_dev,struct iio_chan_spec const *chan, char *label);
  int (*write_raw_get_fmt)(struct iio_dev *indio_dev,struct iio_chan_spec const *chan, long mask);
  int (*read_event_config)(struct iio_dev *indio_dev,const struct iio_chan_spec *chan,enum iio_event_type type, enum iio_event_direction dir);
  int (*write_event_config)(struct iio_dev *indio_dev,const struct iio_chan_spec *chan,enum iio_event_type type,enum iio_event_direction dir, int state);
  int (*read_event_value)(struct iio_dev *indio_dev,const struct iio_chan_spec *chan,enum iio_event_type type,enum iio_event_direction dir, enum iio_event_info info, int *val, int *val2);
  int (*write_event_value)(struct iio_dev *indio_dev,const struct iio_chan_spec *chan,enum iio_event_type type,enum iio_event_direction dir, enum iio_event_info info, int val, int val2);
  int (*validate_trigger)(struct iio_dev *indio_dev, struct iio_trigger *trig);
  int (*update_scan_mode)(struct iio_dev *indio_dev, const unsigned long *scan_mask);
  int (*debugfs_reg_access)(struct iio_dev *indio_dev,unsigned reg, unsigned writeval, unsigned *readval);
  int (*of_xlate)(struct iio_dev *indio_dev, const struct of_phandle_args *iiospec);
  int (*hwfifo_set_watermark)(struct iio_dev *indio_dev, unsigned val);
  int (*hwfifo_flush_to_buffer)(struct iio_dev *indio_dev, unsigned count);
};

Members

event_attrs: event control attributes
attrs: general purpose device attributes
read_raw: function to request a value from the device. mask specifies which value. Note 0 means a reading of the channel in question. Return value will specify the type of value returned by the device. val and val2 will contain the elements making up the returned value.
read_raw_multi: function to return values from the device. mask specifies which value. Note 0 means a reading of the channel in question. Return value will specify the type of value returned by the device. vals pointer contain the elements making up the returned value. max_len specifies maximum number of elements vals pointer can contain. val_len is used to return length of valid elements in vals.
read_avail: function to return the available values from the device. mask specifies which value. Note 0 means the available values for the channel in question. Return value specifies if a IIO_AVAIL_LIST or a IIO_AVAIL_RANGE is returned in vals. The type of the vals are returned in type and the number of vals is returned in length. For ranges, there are always three vals returned; min, step and max. For lists, all possible values are enumerated.
write_raw: function to write a value to the device. Parameters are the same as for read_raw.
read_label: function to request label name for a specified label, for better channel identification.
write_raw_get_fmt: callback function to query the expected format/precision. If not set by the driver, write_raw returns IIO_VAL_INT_PLUS_MICRO.
read_event_config: find out if the event is enabled.
write_event_config: set if the event is enabled.
read_event_value: read a configuration value associated with the event.
write_event_value: write a configuration value for the event.
validate_trigger: function to validate the trigger when the current trigger gets changed.
update_scan_mode: function to configure device and scan buffer when channels have changed
debugfs_reg_access: function to read or write register value of device
of_xlate: function pointer to obtain channel specifier index. When #iio-cells is greater than ‘0’, the driver could provide a custom of_xlate function that reads the args and returns the appropriate index in registered IIO channels array.
hwfifo_set_watermark: function pointer to set the current hardware fifo watermark level; see hwfifo_* entries in Documentation/ABI/testing/sysfs-bus-iio for details on how the hardware fifo operates
hwfifo_flush_to_buffer: function pointer to flush the samples stored in the hardware fifo to the device buffer. The driver should not flush more than count samples. The function must return the number of samples flushed, 0 if no samples were flushed or a negative integer if no samples were flushed and there was an error.

struct iio_buffer_setup_ops¶: buffer setup related callbacks

Definition

struct iio_buffer_setup_ops {
  int (*preenable)(struct iio_dev *);
  int (*postenable)(struct iio_dev *);
  int (*predisable)(struct iio_dev *);
  int (*postdisable)(struct iio_dev *);
  bool (*validate_scan_mask)(struct iio_dev *indio_dev, const unsigned long *scan_mask);
};

Members

preenable: [DRIVER] function to run prior to marking buffer enabled
postenable: [DRIVER] function to run after marking buffer enabled
predisable: [DRIVER] function to run prior to marking buffer disabled
postdisable: [DRIVER] function to run after marking buffer disabled
validate_scan_mask: [DRIVER] function callback to check whether a given scan mask is valid for the device.

struct iio_dev¶: industrial I/O device

Definition

struct iio_dev {
  int modes;
  int currentmode;
  struct device                   dev;
  struct iio_buffer               *buffer;
  int scan_bytes;
  struct mutex                    mlock;
  const unsigned long             *available_scan_masks;
  unsigned masklength;
  const unsigned long             *active_scan_mask;
  bool scan_timestamp;
  struct iio_trigger              *trig;
  struct iio_poll_func            *pollfunc;
  struct iio_poll_func            *pollfunc_event;
  struct iio_chan_spec const      *channels;
  int num_channels;
  const char                      *name;
  const char                      *label;
  const struct iio_info           *info;
  const struct iio_buffer_setup_ops       *setup_ops;
  void *priv;
};

Members

modes: [DRIVER] operating modes supported by device
currentmode: [DRIVER] current operating mode
dev: [DRIVER] device structure, should be assigned a parent and owner
buffer: [DRIVER] any buffer present
scan_bytes: [INTERN] num bytes captured to be fed to buffer demux
mlock: [INTERN] lock used to prevent simultaneous device state changes
available_scan_masks: [DRIVER] optional array of allowed bitmasks
masklength: [INTERN] the length of the mask established from channels
active_scan_mask: [INTERN] union of all scan masks requested by buffers
scan_timestamp: [INTERN] set if any buffers have requested timestamp
trig: [INTERN] current device trigger (buffer modes)
pollfunc: [DRIVER] function run on trigger being received
pollfunc_event: [DRIVER] function run on events trigger being received
channels: [DRIVER] channel specification structure table
num_channels: [DRIVER] number of channels specified in channels.
name: [DRIVER] name of the device.
label: [DRIVER] unique name to identify which device this is
info: [DRIVER] callbacks and constant info from driver
setup_ops: [DRIVER] callbacks to call before and after buffer enable/disable
priv: [DRIVER] reference to driver’s private information MUST be accessed ONLY via iio_priv() helper

iio_device_register¶

iio_device_register (indio_dev)

register a device with the IIO subsystem

Parameters

indio_dev: Device structure filled by the device driver

devm_iio_device_register¶

devm_iio_device_register (dev, indio_dev)

Resource-managed iio_device_register()

Parameters

dev: Device to allocate iio_dev for
indio_dev: Device structure filled by the device driver

Description

Managed iio_device_register. The IIO device registered with this function is automatically unregistered on driver detach. This function calls iio_device_register() internally. Refer to that function for more information.

Return

0 on success, negative error number on failure.

void iio_device_put(struct iio_dev *indio_dev)¶: reference counted deallocation of struct device

Parameters

struct iio_dev *indio_dev: IIO device structure containing the device

struct iio_dev *dev_to_iio_dev(struct device *dev)¶: Get IIO device struct from a device struct

Parameters

struct device *dev: The device embedded in the IIO device

Note

The device must be a IIO device, otherwise the result is undefined.

struct iio_dev *iio_device_get(struct iio_dev *indio_dev)¶: increment reference count for the device

Parameters

struct iio_dev *indio_dev: IIO device structure

Return

The passed IIO device

void iio_device_set_parent(struct iio_dev *indio_dev, struct device *parent)¶: assign parent device to the IIO device object

Parameters

struct iio_dev *indio_dev: IIO device structure
struct device *parent: reference to parent device object

Description

This utility must be called between IIO device allocation (via devm_iio_device_alloc()) & IIO device registration (via iio_device_register() and devm_iio_device_register())). By default, the device allocation will also assign a parent device to the IIO device object. In cases where devm_iio_device_alloc() is used, sometimes the parent device must be different than the device used to manage the allocation. In that case, this helper should be used to change the parent, hence the requirement to call this between allocation & registration.

void iio_device_set_drvdata(struct iio_dev *indio_dev, void *data)¶: Set device driver data

Parameters

struct iio_dev *indio_dev: IIO device structure
void *data: Driver specific data

Description

Allows to attach an arbitrary pointer to an IIO device, which can later be retrieved by iio_device_get_drvdata().

void *iio_device_get_drvdata(const struct iio_dev *indio_dev)¶: Get device driver data

Parameters

const struct iio_dev *indio_dev: IIO device structure

Description

Returns the data previously set with iio_device_set_drvdata()

bool iio_buffer_enabled(struct iio_dev *indio_dev)¶: helper function to test if the buffer is enabled

Parameters

struct iio_dev *indio_dev: IIO device structure for device

struct dentry *iio_get_debugfs_dentry(struct iio_dev *indio_dev)¶: helper function to get the debugfs_dentry

Parameters

struct iio_dev *indio_dev: IIO device structure for device

IIO_DEGREE_TO_RAD¶

IIO_DEGREE_TO_RAD (deg)

Convert degree to rad

Parameters

deg: A value in degree

Description

Returns the given value converted from degree to rad

IIO_RAD_TO_DEGREE¶

IIO_RAD_TO_DEGREE (rad)

Convert rad to degree

Parameters

rad: A value in rad

Description

Returns the given value converted from rad to degree

IIO_G_TO_M_S_2¶

IIO_G_TO_M_S_2 (g)

Convert g to meter / second**2

Parameters

g: A value in g

Description

Returns the given value converted from g to meter / second**2

IIO_M_S_2_TO_G¶

IIO_M_S_2_TO_G (ms2)

Convert meter / second**2 to g

Parameters

ms2: A value in meter / second**2

Description

Returns the given value converted from meter / second**2 to g

int iio_device_id(struct iio_dev *indio_dev)¶: query the unique ID for the device

Parameters

struct iio_dev *indio_dev: Device structure whose ID is being queried

Description

The IIO device ID is a unique index used for example for the naming of the character device /dev/iio:device[ID]

int iio_device_set_clock(struct iio_dev *indio_dev, clockid_t clock_id)¶: Set current timestamping clock for the device

Parameters

struct iio_dev *indio_dev: IIO device structure containing the device
clockid_t clock_id: timestamping clock posix identifier to set.

clockid_t iio_device_get_clock(const struct iio_dev *indio_dev)¶: Retrieve current timestamping clock for the device

Parameters

const struct iio_dev *indio_dev: IIO device structure containing the device

s64 iio_get_time_ns(const struct iio_dev *indio_dev)¶: utility function to get a time stamp for events etc

Parameters

const struct iio_dev *indio_dev: device

unsigned int iio_get_time_res(const struct iio_dev *indio_dev)¶: utility function to get time stamp clock resolution in nano seconds.

Parameters

const struct iio_dev *indio_dev: device

int iio_read_mount_matrix(struct device *dev, struct iio_mount_matrix *matrix)¶: retrieve iio device mounting matrix from device “mount-matrix” property

Parameters

struct device *dev: device the mounting matrix property is assigned to
struct iio_mount_matrix *matrix: where to store retrieved matrix

Description

If device is assigned no mounting matrix property, a default 3x3 identity matrix will be filled in.

Return

0 if success, or a negative error code on failure.

ssize_t iio_format_value(char *buf, unsigned int type, int size, int *vals)¶: Formats a IIO value into its string representation

Parameters

char *buf: The buffer to which the formatted value gets written which is assumed to be big enough (i.e. PAGE_SIZE).
unsigned int type: One of the IIO_VAL_* constants. This decides how the val and val2 parameters are formatted.
int size: Number of IIO value entries contained in vals
int *vals: Pointer to the values, exact meaning depends on the type parameter.

Return

0 by default, a negative number on failure or the: total number of characters written for a type that belongs to the IIO_VAL_* constant.

int iio_str_to_fixpoint(const char *str, int fract_mult, int *integer, int *fract)¶: Parse a fixed-point number from a string

Parameters

const char *str: The string to parse
int fract_mult: Multiplier for the first decimal place, should be a power of 10
int *integer: The integer part of the number
int *fract: The fractional part of the number

Description

Returns 0 on success, or a negative error code if the string could not be parsed.

struct iio_dev *iio_device_alloc(struct device *parent, int sizeof_priv)¶: allocate an iio_dev from a driver

Parameters

struct device *parent: Parent device.
int sizeof_priv: Space to allocate for private structure.

void iio_device_free(struct iio_dev *dev)¶: free an iio_dev from a driver

Parameters

struct iio_dev *dev: the iio_dev associated with the device

struct iio_dev *devm_iio_device_alloc(struct device *parent, int sizeof_priv)¶: Resource-managed iio_device_alloc()

Parameters

struct device *parent: Device to allocate iio_dev for, and parent for this IIO device
int sizeof_priv: Space to allocate for private structure.

Description

Managed iio_device_alloc. iio_dev allocated with this function is automatically freed on driver detach.

Return

Pointer to allocated iio_dev on success, NULL on failure.

void iio_device_unregister(struct iio_dev *indio_dev)¶: unregister a device from the IIO subsystem

Parameters

struct iio_dev *indio_dev: Device structure representing the device.

int iio_device_claim_direct_mode(struct iio_dev *indio_dev)¶: Keep device in direct mode

Parameters

struct iio_dev *indio_dev: the iio_dev associated with the device

Description

If the device is in direct mode it is guaranteed to stay that way until iio_device_release_direct_mode() is called.

Use with iio_device_release_direct_mode()

Return

0 on success, -EBUSY on failure

void iio_device_release_direct_mode(struct iio_dev *indio_dev)¶: releases claim on direct mode

Parameters

struct iio_dev *indio_dev: the iio_dev associated with the device

Description

Release the claim. Device is no longer guaranteed to stay in direct mode.

Use with iio_device_claim_direct_mode()