i2c_master_send(9)

💅 i2c_master_send(9)

okay so welcome to the Kernel API Manual bestie, and today's main character is i2c_master_send — the little function that could, and does, one message at a time. let me put you on 🫶

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✨ NAME ✨

i2c_master_send — issue a single I2C message in master transmit mode

like literally just one (1) message, in master transmit mode, that's the whole job and she does it flawlessly 😌

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🦋 SYNOPSIS 🦋

int i2c_master_send (const struct i2c_client *client , const char *buf ,
int count );

the signature is giving "three args and a dream" and honestly? iconic.

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🎀 ARGUMENTS 🎀

• client — handle to the slave device. this is your little guy, your target, your pen pal on the bus 💌
• buf — the data that will be written to the slave. the actual payload, the ~content~, the message itself ✨
• count — how many bytes to write. must be less than 64k, because msg.len is u16 — no cap, that's just the type fr fr. keep it under 64k or the universe (and the u16) says no 🙈

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🌸 DESCRIPTION 🌸

returns a negative errno, or else the number of bytes written.

that's it. that's the whole description. she's a simple queen with a simple contract: negative errno = something went sideways 😭, anything else = how many bytes actually got written 💖

no cap, read that return value. it's the whole plot.

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👑 SEE ALSO 👑

• kernel file ./include/linux/i2c.h — the source of truth, go read her 📖

and the whole extended friend group, in the order the manual lists them:

• i2c_master_recv(9)
• i2c_master_recv_dmasafe(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_algorithm(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)

go follow all of them, they're all in ./include/linux and they're all slay in their own way 🌈

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mwah 💋 that's the page! brought to you by ./include/linux, dated October 2026, and of course the one and only i2c_master_send(9) — go send exactly one message bestie, you've got this 💜