I²C and SMBus Subsystem¶

I²C (or without fancy typography, “I2C”) is an acronym for the “Inter-IC” bus, a simple bus protocol which is widely used where low data rate communications suffice. Since it’s also a licensed trademark, some vendors use another name (such as “Two-Wire Interface”, TWI) for the same bus. I2C only needs two signals (SCL for clock, SDA for data), conserving board real estate and minimizing signal quality issues. Most I2C devices use seven bit addresses, and bus speeds of up to 400 kHz; there’s a high speed extension (3.4 MHz) that’s not yet found wide use. I2C is a multi-master bus; open drain signaling is used to arbitrate between masters, as well as to handshake and to synchronize clocks from slower clients.

The Linux I2C programming interfaces support the master side of bus interactions and the slave side. The programming interface is structured around two kinds of driver, and two kinds of device. An I2C “Adapter Driver” abstracts the controller hardware; it binds to a physical device (perhaps a PCI device or platform_device) and exposes a struct i2c_adapter representing each I2C bus segment it manages. On each I2C bus segment will be I2C devices represented by a struct i2c_client. Those devices will be bound to a struct i2c_driver, which should follow the standard Linux driver model. There are functions to perform various I2C protocol operations; at this writing all such functions are usable only from task context.

The System Management Bus (SMBus) is a sibling protocol. Most SMBus systems are also I2C conformant. The electrical constraints are tighter for SMBus, and it standardizes particular protocol messages and idioms. Controllers that support I2C can also support most SMBus operations, but SMBus controllers don’t support all the protocol options that an I2C controller will. There are functions to perform various SMBus protocol operations, either using I2C primitives or by issuing SMBus commands to i2c_adapter devices which don’t support those I2C operations.

struct i2c_driver¶: represent an I2C device driver

Definition

struct i2c_driver {
  unsigned int class;
  int (* attach_adapter) (struct i2c_adapter *);
  int (* probe) (struct i2c_client *, const struct i2c_device_id *);
  int (* remove) (struct i2c_client *);
  int (* probe_new) (struct i2c_client *);
  void (* shutdown) (struct i2c_client *);
  void (* alert) (struct i2c_client *, enum i2c_alert_protocol protocol, unsigned int data);
  int (* command) (struct i2c_client *client, unsigned int cmd, void *arg);
  struct device_driver driver;
  const struct i2c_device_id * id_table;
  int (* detect) (struct i2c_client *, struct i2c_board_info *);
  const unsigned short * address_list;
  struct list_head clients;
  bool disable_i2c_core_irq_mapping;
};

Members

class: What kind of i2c device we instantiate (for detect)
attach_adapter: Callback for bus addition (deprecated)
probe: Callback for device binding - soon to be deprecated
remove: Callback for device unbinding
probe_new: New callback for device binding
shutdown: Callback for device shutdown
alert: Alert callback, for example for the SMBus alert protocol
command: Callback for bus-wide signaling (optional)
driver: Device driver model driver
id_table: List of I2C devices supported by this driver
detect: Callback for device detection
address_list: The I2C addresses to probe (for detect)
clients: List of detected clients we created (for i2c-core use only)
disable_i2c_core_irq_mapping: Tell the i2c-core to not do irq-mapping

Description

The driver.owner field should be set to the module owner of this driver. The driver.name field should be set to the name of this driver.

For automatic device detection, both detect and address_list must be defined. class should also be set, otherwise only devices forced with module parameters will be created. The detect function must fill at least the name field of the i2c_board_info structure it is handed upon successful detection, and possibly also the flags field.

If detect is missing, the driver will still work fine for enumerated devices. Detected devices simply won’t be supported. This is expected for the many I2C/SMBus devices which can’t be detected reliably, and the ones which can always be enumerated in practice.

The i2c_client structure which is handed to the detect callback is not a real i2c_client. It is initialized just enough so that you can call i2c_smbus_read_byte_data and friends on it. Don’t do anything else with it. In particular, calling dev_dbg and friends on it is not allowed.

struct i2c_client¶: represent an I2C slave device

Definition

struct i2c_client {
  unsigned short flags;
  unsigned short addr;
  char name;
  struct i2c_adapter * adapter;
  struct device dev;
  int irq;
  struct list_head detected;
#if IS_ENABLED(CONFIG_I2C_SLAVE
  i2c_slave_cb_t slave_cb;
#endif
};

Members

flags: I2C_CLIENT_TEN indicates the device uses a ten bit chip address; I2C_CLIENT_PEC indicates it uses SMBus Packet Error Checking
addr: Address used on the I2C bus connected to the parent adapter.
name: Indicates the type of the device, usually a chip name that’s generic enough to hide second-sourcing and compatible revisions.
adapter: manages the bus segment hosting this I2C device
dev: Driver model device node for the slave.
irq: indicates the IRQ generated by this device (if any)
detected: member of an i2c_driver.clients list or i2c-core’s userspace_devices list
slave_cb: Callback when I2C slave mode of an adapter is used. The adapter calls it to pass on slave events to the slave driver.

Description

An i2c_client identifies a single device (i.e. chip) connected to an i2c bus. The behaviour exposed to Linux is defined by the driver managing the device.

struct i2c_board_info¶: template for device creation

Definition

struct i2c_board_info {
  char type;
  unsigned short flags;
  unsigned short addr;
  void * platform_data;
  struct dev_archdata * archdata;
  struct device_node * of_node;
  struct fwnode_handle * fwnode;
  const struct property_entry * properties;
  const struct resource * resources;
  unsigned int num_resources;
  int irq;
};

Members

type: chip type, to initialize i2c_client.name
flags: to initialize i2c_client.flags
addr: stored in i2c_client.addr
platform_data: stored in i2c_client.dev.platform_data
archdata: copied into i2c_client.dev.archdata
of_node: pointer to OpenFirmware device node
fwnode: device node supplied by the platform firmware
properties: additional device properties for the device
resources: resources associated with the device
num_resources: number of resources in the resources array
irq: stored in i2c_client.irq

Description

I2C doesn’t actually support hardware probing, although controllers and devices may be able to use I2C_SMBUS_QUICK to tell whether or not there’s a device at a given address. Drivers commonly need more information than that, such as chip type, configuration, associated IRQ, and so on.

i2c_board_info is used to build tables of information listing I2C devices that are present. This information is used to grow the driver model tree. For mainboards this is done statically using i2c_register_board_info(); bus numbers identify adapters that aren’t yet available. For add-on boards, i2c_new_device() does this dynamically with the adapter already known.

I2C_BOARD_INFO(dev_type, dev_addr)¶: macro used to list an i2c device and its address

Parameters

dev_type: identifies the device type
dev_addr: the device’s address on the bus.

Description

This macro initializes essential fields of a struct i2c_board_info, declaring what has been provided on a particular board. Optional fields (such as associated irq, or device-specific platform_data) are provided using conventional syntax.

struct i2c_algorithm¶: represent I2C transfer method

Definition

struct i2c_algorithm {
  int (* master_xfer) (struct i2c_adapter *adap, struct i2c_msg *msgs, int num);
  int (* smbus_xfer) (struct i2c_adapter *adap, u16 addr,unsigned short flags, char read_write, u8 command, int size, union i2c_smbus_data *data);
  u32 (* functionality) (struct i2c_adapter *);
#if IS_ENABLED(CONFIG_I2C_SLAVE
  int (* reg_slave) (struct i2c_client *client);
  int (* unreg_slave) (struct i2c_client *client);
#endif
};

Members

master_xfer: Issue a set of i2c transactions to the given I2C adapter defined by the msgs array, with num messages available to transfer via the adapter specified by adap.
smbus_xfer: Issue smbus transactions to the given I2C adapter. If this is not present, then the bus layer will try and convert the SMBus calls into I2C transfers instead.
functionality: Return the flags that this algorithm/adapter pair supports from the I2C_FUNC_* flags.
reg_slave: Register given client to I2C slave mode of this adapter
unreg_slave: Unregister given client from I2C slave mode of this adapter

Description

The following structs are for those who like to implement new bus drivers: i2c_algorithm is the interface to a class of hardware solutions which can be addressed using the same bus algorithms - i.e. bit-banging or the PCF8584 to name two of the most common.

The return codes from the master_xfer field should indicate the type of error code that occurred during the transfer, as documented in the kernel Documentation file Documentation/i2c/fault-codes.

struct i2c_lock_operations¶: represent I2C locking operations

Definition

struct i2c_lock_operations {
  void (* lock_bus) (struct i2c_adapter *, unsigned int flags);
  int (* trylock_bus) (struct i2c_adapter *, unsigned int flags);
  void (* unlock_bus) (struct i2c_adapter *, unsigned int flags);
};

Members

lock_bus: Get exclusive access to an I2C bus segment
trylock_bus: Try to get exclusive access to an I2C bus segment
unlock_bus: Release exclusive access to an I2C bus segment

Description

The main operations are wrapped by i2c_lock_bus and i2c_unlock_bus.

struct i2c_timings¶: I2C timing information

Definition

struct i2c_timings {
  u32 bus_freq_hz;
  u32 scl_rise_ns;
  u32 scl_fall_ns;
  u32 scl_int_delay_ns;
  u32 sda_fall_ns;
};

Members

bus_freq_hz: the bus frequency in Hz
scl_rise_ns: time SCL signal takes to rise in ns; t(r) in the I2C specification
scl_fall_ns: time SCL signal takes to fall in ns; t(f) in the I2C specification
scl_int_delay_ns: time IP core additionally needs to setup SCL in ns
sda_fall_ns: time SDA signal takes to fall in ns; t(f) in the I2C specification

struct i2c_bus_recovery_info¶: I2C bus recovery information

Definition

struct i2c_bus_recovery_info {
  int (* recover_bus) (struct i2c_adapter *);
  int (* get_scl) (struct i2c_adapter *);
  void (* set_scl) (struct i2c_adapter *, int val);
  int (* get_sda) (struct i2c_adapter *);
  void (* prepare_recovery) (struct i2c_adapter *);
  void (* unprepare_recovery) (struct i2c_adapter *);
  int scl_gpio;
  int sda_gpio;
};

Members

recover_bus: Recover routine. Either pass driver’s recover_bus() routine, or i2c_generic_scl_recovery() or i2c_generic_gpio_recovery().
get_scl: This gets current value of SCL line. Mandatory for generic SCL recovery. Used internally for generic GPIO recovery.
set_scl: This sets/clears SCL line. Mandatory for generic SCL recovery. Used internally for generic GPIO recovery.
get_sda: This gets current value of SDA line. Optional for generic SCL recovery. Used internally, if sda_gpio is a valid GPIO, for generic GPIO recovery.
prepare_recovery: This will be called before starting recovery. Platform may configure padmux here for SDA/SCL line or something else they want.
unprepare_recovery: This will be called after completing recovery. Platform may configure padmux here for SDA/SCL line or something else they want.
scl_gpio: gpio number of the SCL line. Only required for GPIO recovery.
sda_gpio: gpio number of the SDA line. Only required for GPIO recovery.

struct i2c_adapter_quirks¶: describe flaws of an i2c adapter

Definition

struct i2c_adapter_quirks {
  u64 flags;
  int max_num_msgs;
  u16 max_write_len;
  u16 max_read_len;
  u16 max_comb_1st_msg_len;
  u16 max_comb_2nd_msg_len;
};

Members

flags: see I2C_AQ_* for possible flags and read below
max_num_msgs: maximum number of messages per transfer
max_write_len: maximum length of a write message
max_read_len: maximum length of a read message
max_comb_1st_msg_len: maximum length of the first msg in a combined message
max_comb_2nd_msg_len: maximum length of the second msg in a combined message

Description

Note about combined messages: Some I2C controllers can only send one message per transfer, plus something called combined message or write-then-read. This is (usually) a small write message followed by a read message and barely enough to access register based devices like EEPROMs. There is a flag to support this mode. It implies max_num_msg = 2 and does the length checks with max_comb_*_len because combined message mode usually has its own limitations. Because of HW implementations, some controllers can actually do write-then-anything or other variants. To support that, write-then-read has been broken out into smaller bits like write-first and read-second which can be combined as needed.

void i2c_lock_bus(struct i2c_adapter * adapter, unsigned int flags)¶: Get exclusive access to an I2C bus segment

Parameters

struct i2c_adapter * adapter: Target I2C bus segment
unsigned int flags: I2C_LOCK_ROOT_ADAPTER locks the root i2c adapter, I2C_LOCK_SEGMENT locks only this branch in the adapter tree

int i2c_trylock_bus(struct i2c_adapter * adapter, unsigned int flags)¶: Try to get exclusive access to an I2C bus segment

Parameters

struct i2c_adapter * adapter: Target I2C bus segment
unsigned int flags: I2C_LOCK_ROOT_ADAPTER tries to locks the root i2c adapter, I2C_LOCK_SEGMENT tries to lock only this branch in the adapter tree

Return

true if the I2C bus segment is locked, false otherwise

void i2c_unlock_bus(struct i2c_adapter * adapter, unsigned int flags)¶: Release exclusive access to an I2C bus segment

Parameters

struct i2c_adapter * adapter: Target I2C bus segment
unsigned int flags: I2C_LOCK_ROOT_ADAPTER unlocks the root i2c adapter, I2C_LOCK_SEGMENT unlocks only this branch in the adapter tree

bool i2c_check_quirks(struct i2c_adapter * adap, u64 quirks)¶: Function for checking the quirk flags in an i2c adapter

Parameters

struct i2c_adapter * adap: i2c adapter
u64 quirks: quirk flags

Return

true if the adapter has all the specified quirk flags, false if not

module_i2c_driver(__i2c_driver)¶: Helper macro for registering a modular I2C driver

Parameters

__i2c_driver: i2c_driver struct

Description

Helper macro for I2C drivers which do not do anything special in module init/exit. This eliminates a lot of boilerplate. Each module may only use this macro once, and calling it replaces module_init() and module_exit()

builtin_i2c_driver(__i2c_driver)¶: Helper macro for registering a builtin I2C driver

Parameters

__i2c_driver: i2c_driver struct

Description

Helper macro for I2C drivers which do not do anything special in their init. This eliminates a lot of boilerplate. Each driver may only use this macro once, and calling it replaces device_initcall().

int i2c_register_board_info(int busnum, struct i2c_board_info const * info, unsigned len)¶: statically declare I2C devices

Parameters

int busnum: identifies the bus to which these devices belong
struct i2c_board_info const * info: vector of i2c device descriptors
unsigned len: how many descriptors in the vector; may be zero to reserve the specified bus number.

Description

Systems using the Linux I2C driver stack can declare tables of board info while they initialize. This should be done in board-specific init code near arch_initcall() time, or equivalent, before any I2C adapter driver is registered. For example, mainboard init code could define several devices, as could the init code for each daughtercard in a board stack.

The I2C devices will be created later, after the adapter for the relevant bus has been registered. After that moment, standard driver model tools are used to bind “new style” I2C drivers to the devices. The bus number for any device declared using this routine is not available for dynamic allocation.

The board info passed can safely be __initdata, but be careful of embedded pointers (for platform_data, functions, etc) since that won’t be copied. Device properties are deep-copied though.

struct i2c_client * i2c_verify_client(struct device * dev)¶: return parameter as i2c_client, or NULL

Parameters

struct device * dev: device, probably from some driver model iterator

Description

When traversing the driver model tree, perhaps using driver model iterators like device_for_each_child(), you can’t assume very much about the nodes you find. Use this function to avoid oopses caused by wrongly treating some non-I2C device as an i2c_client.

struct i2c_client * i2c_new_device(struct i2c_adapter * adap, struct i2c_board_info const * info)¶: instantiate an i2c device

Parameters

struct i2c_adapter * adap: the adapter managing the device
struct i2c_board_info const * info: describes one I2C device; bus_num is ignored

Context

can sleep

Description

Create an i2c device. Binding is handled through driver model probe()/remove() methods. A driver may be bound to this device when we return from this function, or any later moment (e.g. maybe hotplugging will load the driver module). This call is not appropriate for use by mainboard initialization logic, which usually runs during an arch_initcall() long before any i2c_adapter could exist.

This returns the new i2c client, which may be saved for later use with i2c_unregister_device(); or NULL to indicate an error.

void i2c_unregister_device(struct i2c_client * client)¶: reverse effect of i2c_new_device()

Parameters

struct i2c_client * client: value returned from i2c_new_device()

Context

can sleep

struct i2c_client * i2c_new_dummy(struct i2c_adapter * adapter, u16 address)¶: return a new i2c device bound to a dummy driver

Parameters

struct i2c_adapter * adapter: the adapter managing the device
u16 address: seven bit address to be used

Context

can sleep

Description

This returns an I2C client bound to the “dummy” driver, intended for use with devices that consume multiple addresses. Examples of such chips include various EEPROMS (like 24c04 and 24c08 models).

These dummy devices have two main uses. First, most I2C and SMBus calls except i2c_transfer() need a client handle; the dummy will be that handle. And second, this prevents the specified address from being bound to a different driver.

This returns the new i2c client, which should be saved for later use with i2c_unregister_device(); or NULL to indicate an error.

struct i2c_client * i2c_new_secondary_device(struct i2c_client * client, const char * name, u16 default_addr)¶: Helper to get the instantiated secondary address and create the associated device

Parameters

struct i2c_client * client: Handle to the primary client
const char * name: Handle to specify which secondary address to get
u16 default_addr: Used as a fallback if no secondary address was specified

Context

can sleep

Description

I2C clients can be composed of multiple I2C slaves bound together in a single component. The I2C client driver then binds to the master I2C slave and needs to create I2C dummy clients to communicate with all the other slaves.

This function creates and returns an I2C dummy client whose I2C address is retrieved from the platform firmware based on the given slave name. If no address is specified by the firmware default_addr is used.

On DT-based platforms the address is retrieved from the “reg” property entry cell whose “reg-names” value matches the slave name.

This returns the new i2c client, which should be saved for later use with i2c_unregister_device(); or NULL to indicate an error.

struct i2c_adapter * i2c_verify_adapter(struct device * dev)¶: return parameter as i2c_adapter or NULL

Parameters

struct device * dev: device, probably from some driver model iterator

Description

When traversing the driver model tree, perhaps using driver model iterators like device_for_each_child(), you can’t assume very much about the nodes you find. Use this function to avoid oopses caused by wrongly treating some non-I2C device as an i2c_adapter.

int i2c_handle_smbus_host_notify(struct i2c_adapter * adap, unsigned short addr)¶: Forward a Host Notify event to the correct I2C client.

Parameters

struct i2c_adapter * adap: the adapter
unsigned short addr: the I2C address of the notifying device

Context

can’t sleep

Description

Helper function to be called from an I2C bus driver’s interrupt handler. It will schedule the Host Notify IRQ.

int i2c_add_adapter(struct i2c_adapter * adapter)¶: declare i2c adapter, use dynamic bus number

Parameters

struct i2c_adapter * adapter: the adapter to add

Context

can sleep

Description

This routine is used to declare an I2C adapter when its bus number doesn’t matter or when its bus number is specified by an dt alias. Examples of bases when the bus number doesn’t matter: I2C adapters dynamically added by USB links or PCI plugin cards.

When this returns zero, a new bus number was allocated and stored in adap->nr, and the specified adapter became available for clients. Otherwise, a negative errno value is returned.

int i2c_add_numbered_adapter(struct i2c_adapter * adap)¶: declare i2c adapter, use static bus number

Parameters

struct i2c_adapter * adap: the adapter to register (with adap->nr initialized)

Context

can sleep

Description

This routine is used to declare an I2C adapter when its bus number matters. For example, use it for I2C adapters from system-on-chip CPUs, or otherwise built in to the system’s mainboard, and where i2c_board_info is used to properly configure I2C devices.

If the requested bus number is set to -1, then this function will behave identically to i2c_add_adapter, and will dynamically assign a bus number.

If no devices have pre-been declared for this bus, then be sure to register the adapter before any dynamically allocated ones. Otherwise the required bus ID may not be available.

When this returns zero, the specified adapter became available for clients using the bus number provided in adap->nr. Also, the table of I2C devices pre-declared using i2c_register_board_info() is scanned, and the appropriate driver model device nodes are created. Otherwise, a negative errno value is returned.

void i2c_del_adapter(struct i2c_adapter * adap)¶: unregister I2C adapter

Parameters

struct i2c_adapter * adap: the adapter being unregistered

Context

can sleep

Description

This unregisters an I2C adapter which was previously registered by i2c_add_adapter or i2c_add_numbered_adapter.

void i2c_parse_fw_timings(struct device * dev, struct i2c_timings * t, bool use_defaults)¶: get I2C related timing parameters from firmware

Parameters

struct device * dev: The device to scan for I2C timing properties
struct i2c_timings * t: the i2c_timings struct to be filled with values
bool use_defaults: bool to use sane defaults derived from the I2C specification when properties are not found, otherwise use 0

Description

Scan the device for the generic I2C properties describing timing parameters for the signal and fill the given struct with the results. If a property was not found and use_defaults was true, then maximum timings are assumed which are derived from the I2C specification. If use_defaults is not used, the results will be 0, so drivers can apply their own defaults later. The latter is mainly intended for avoiding regressions of existing drivers which want to switch to this function. New drivers almost always should use the defaults.

void i2c_del_driver(struct i2c_driver * driver)¶: unregister I2C driver

Parameters

struct i2c_driver * driver: the driver being unregistered

Context

can sleep

struct i2c_client * i2c_use_client(struct i2c_client * client)¶: increments the reference count of the i2c client structure

Parameters

struct i2c_client * client: the client being referenced

Description

Each live reference to a client should be refcounted. The driver model does that automatically as part of driver binding, so that most drivers don’t need to do this explicitly: they hold a reference until they’re unbound from the device.

A pointer to the client with the incremented reference counter is returned.

void i2c_release_client(struct i2c_client * client)¶: release a use of the i2c client structure

Parameters

struct i2c_client * client: the client being no longer referenced

Description

Must be called when a user of a client is finished with it.

int __i2c_transfer(struct i2c_adapter * adap, struct i2c_msg * msgs, int num)¶: unlocked flavor of i2c_transfer

Parameters

struct i2c_adapter * adap: Handle to I2C bus
struct i2c_msg * msgs: One or more messages to execute before STOP is issued to terminate the operation; each message begins with a START.
int num: Number of messages to be executed.

Description

Returns negative errno, else the number of messages executed.

Adapter lock must be held when calling this function. No debug logging takes place. adap->algo->master_xfer existence isn’t checked.

int i2c_transfer(struct i2c_adapter * adap, struct i2c_msg * msgs, int num)¶: execute a single or combined I2C message

Parameters

struct i2c_adapter * adap: Handle to I2C bus
struct i2c_msg * msgs: One or more messages to execute before STOP is issued to terminate the operation; each message begins with a START.
int num: Number of messages to be executed.

Description

Returns negative errno, else the number of messages executed.

Note that there is no requirement that each message be sent to the same slave address, although that is the most common model.

int i2c_master_send(const struct i2c_client * client, const char * buf, int count)¶: issue a single I2C message in master transmit mode

Parameters

const struct i2c_client * client: Handle to slave device
const char * buf: Data that will be written to the slave
int count: How many bytes to write, must be less than 64k since msg.len is u16

Description

Returns negative errno, or else the number of bytes written.

int i2c_master_recv(const struct i2c_client * client, char * buf, int count)¶: issue a single I2C message in master receive mode

Parameters

const struct i2c_client * client: Handle to slave device
char * buf: Where to store data read from slave
int count: How many bytes to read, must be less than 64k since msg.len is u16

Description

Returns negative errno, or else the number of bytes read.

s32 i2c_smbus_read_byte(const struct i2c_client * client)¶: SMBus “receive byte” protocol

Parameters

const struct i2c_client * client: Handle to slave device

Description

This executes the SMBus “receive byte” protocol, returning negative errno else the byte received from the device.

s32 i2c_smbus_write_byte(const struct i2c_client * client, u8 value)¶: SMBus “send byte” protocol

Parameters

const struct i2c_client * client: Handle to slave device
u8 value: Byte to be sent

Description

This executes the SMBus “send byte” protocol, returning negative errno else zero on success.

s32 i2c_smbus_read_byte_data(const struct i2c_client * client, u8 command)¶: SMBus “read byte” protocol

Parameters

const struct i2c_client * client: Handle to slave device
u8 command: Byte interpreted by slave

Description

This executes the SMBus “read byte” protocol, returning negative errno else a data byte received from the device.

s32 i2c_smbus_write_byte_data(const struct i2c_client * client, u8 command, u8 value)¶: SMBus “write byte” protocol

Parameters

const struct i2c_client * client: Handle to slave device
u8 command: Byte interpreted by slave
u8 value: Byte being written

Description

This executes the SMBus “write byte” protocol, returning negative errno else zero on success.

s32 i2c_smbus_read_word_data(const struct i2c_client * client, u8 command)¶: SMBus “read word” protocol

Parameters

const struct i2c_client * client: Handle to slave device
u8 command: Byte interpreted by slave

Description

This executes the SMBus “read word” protocol, returning negative errno else a 16-bit unsigned “word” received from the device.

s32 i2c_smbus_write_word_data(const struct i2c_client * client, u8 command, u16 value)¶: SMBus “write word” protocol

Parameters

const struct i2c_client * client: Handle to slave device
u8 command: Byte interpreted by slave
u16 value: 16-bit “word” being written

Description

This executes the SMBus “write word” protocol, returning negative errno else zero on success.

s32 i2c_smbus_read_block_data(const struct i2c_client * client, u8 command, u8 * values)¶: SMBus “block read” protocol

Parameters

const struct i2c_client * client: Handle to slave device
u8 command: Byte interpreted by slave
u8 * values: Byte array into which data will be read; big enough to hold the data returned by the slave. SMBus allows at most 32 bytes.

Description

This executes the SMBus “block read” protocol, returning negative errno else the number of data bytes in the slave’s response.

Note that using this function requires that the client’s adapter support the I2C_FUNC_SMBUS_READ_BLOCK_DATA functionality. Not all adapter drivers support this; its emulation through I2C messaging relies on a specific mechanism (I2C_M_RECV_LEN) which may not be implemented.

s32 i2c_smbus_write_block_data(const struct i2c_client * client, u8 command, u8 length, const u8 * values)¶: SMBus “block write” protocol

Parameters

const struct i2c_client * client: Handle to slave device
u8 command: Byte interpreted by slave
u8 length: Size of data block; SMBus allows at most 32 bytes
const u8 * values: Byte array which will be written.

Description

This executes the SMBus “block write” protocol, returning negative errno else zero on success.

s32 i2c_smbus_xfer(struct i2c_adapter * adapter, u16 addr, unsigned short flags, char read_write, u8 command, int protocol, union i2c_smbus_data * data)¶: execute SMBus protocol operations

Parameters

struct i2c_adapter * adapter: Handle to I2C bus
u16 addr: Address of SMBus slave on that bus
unsigned short flags: I2C_CLIENT_* flags (usually zero or I2C_CLIENT_PEC)
char read_write: I2C_SMBUS_READ or I2C_SMBUS_WRITE
u8 command: Byte interpreted by slave, for protocols which use such bytes
int protocol: SMBus protocol operation to execute, such as I2C_SMBUS_PROC_CALL
union i2c_smbus_data * data: Data to be read or written

Description

This executes an SMBus protocol operation, and returns a negative errno code else zero on success.

s32 i2c_smbus_read_i2c_block_data_or_emulated(const struct i2c_client * client, u8 command, u8 length, u8 * values)¶: read block or emulate

Parameters

const struct i2c_client * client: Handle to slave device
u8 command: Byte interpreted by slave
u8 length: Size of data block; SMBus allows at most I2C_SMBUS_BLOCK_MAX bytes
u8 * values: Byte array into which data will be read; big enough to hold the data returned by the slave. SMBus allows at most I2C_SMBUS_BLOCK_MAX bytes.

Description

This executes the SMBus “block read” protocol if supported by the adapter. If block read is not supported, it emulates it using either word or byte read protocols depending on availability.

The addresses of the I2C slave device that are accessed with this function must be mapped to a linear region, so that a block read will have the same effect as a byte read. Before using this function you must double-check if the I2C slave does support exchanging a block transfer with a byte transfer.

I2C and SMBus Subsystem¶

I²C and SMBus Subsystem¶