STRUCT I2C_ALGORITHM(9)

okay so this is the struct i2c_algorithm(9) page from the Kernel API Manual, and bestie it is literally the blueprint for I2C transfer methods 💖✨

💖 NAME 💖

struct i2c_algorithm — represent I2C transfer methods 🫶

✨ SYNOPSIS ✨

       struct i2c_algorithm {
           union {
             int (*xfer)(struct i2c_adapter *adap, struct i2c_msg *msgs, int
       num);
             int (*master_xfer)(struct i2c_adapter *adap, struct i2c_msg *msgs,
       int num);
           };
           union {
             int (*xfer_atomic)(struct i2c_adapter *adap, struct i2c_msg *msgs,
       int num);
             int (*master_xfer_atomic)(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);
           int (*smbus_xfer_atomic)(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 *adap);
         #if IS_ENABLED(CONFIG_I2C_SLAVE);
           union {
             int (*reg_target)(struct i2c_client *client);
             int (*reg_slave)(struct i2c_client *client);
           };
           union {
             int (*unreg_target)(struct i2c_client *client);
             int (*unreg_slave)(struct i2c_client *client);
           };
         #endif;
        };

🎀 Members 🎀

okay so here's the member-by-member vibe check, bestie 👑

• {unnamed_union} — anonymous
• xfer — Transfer a given number of messages defined by the msgs array via the specified adapter.
• master_xfer — deprecated, use xfer
• {unnamed_union} — anonymous
• xfer_atomic — Same as xfer. Yet, only using atomic context so e.g. PMICs can be accessed very late before shutdown. Optional.
• master_xfer_atomic — deprecated, use xfer_atomic
• 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.
• smbus_xfer_atomic — Same as smbus_xfer. Yet, only using atomic context so e.g. PMICs can be accessed very late before shutdown. Optional.
• functionality — Return the flags that this algorithm/adapter pair supports from the I2C_FUNC_* flags.
• {unnamed_union} — anonymous
• reg_target — Register given client to local target mode of this adapter
• reg_slave — deprecated, use reg_target
• {unnamed_union} — anonymous
• unreg_target — Unregister given client from local target mode of this adapter
• unreg_slave — deprecated, use unreg_target

🌸 Description 🌸

okay so 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. No cap. 🧚

The return codes from the xfer{_atomic} fields should indicate the type of error code that occurred during the transfer, as documented in the Kernel Documentation file Documentation/i2c/fault-codes.rst. Otherwise, the number of messages executed should be returned. 💅

🔥 SEE ALSO 🔥

Kernel file: ./include/linux/i2c.h. Also, the bestie reading list is iconic:

• i2c_master_recv(9)
• i2c_master_recv_dmasafe(9)
• i2c_master_send(9)
• i2c_master_send_dmasafe(9)
• struct i2c_device_identity(9)
• enum i2c_driver_flags(9)
• struct i2c_driver(9)
• struct i2c_client(9)
• struct i2c_board_info(9)
• I2C_BOARD_INFO(9)
• struct i2c_lock_operations(9)
• struct i2c_timings(9)
• struct i2c_bus_recovery_info(9)
• struct i2c_adapter_quirks(9)
• i2c_lock_bus(9)
• i2c_trylock_bus(9)
• i2c_unlock_bus(9)
• i2c_mark_adapter_suspended(9)
• i2c_mark_adapter_resumed(9)
• i2c_check_quirks(9)
• module_i2c_driver(9)
• builtin_i2c_driver(9)

okay that's the whole page, bestie 🫶 it comes from ./include/linux, dated October 2026, and the title is struct i2c_algorithm(9) — periodt 💅🎀