i2c_add_numbered_adapter(9)

i2c_add_numbered_adapter(9) — Kernel API Manual 💅✨

✨ NAME ✨

i2c_add_numbered_adapter — declare i2c adapter, use static bus number. bestie, this is the “my bus number is not a vibe, it’s a fixed address” routine 🎀

🌸 SYNOPSIS 🌸

int i2c_add_numbered_adapter (struct i2c_adapter *adap );

🎀 ARGUMENTS 🎀

• adap — the adapter to register, and yes, it has to have adap->nr initialized already. no cap, bestie, set that number first 💅

😴 CONTEXT 😴

It can sleep 😴. That’s the whole context note, periodt.

💖 DESCRIPTION 💖

okay so 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. it’s giving “I’m built in and I know my number” 🦋

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. literally same behavior, it just picks one for you ✨

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. ⚠️ like, do not skip this ordering step, bestie — it’s important.

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. 🫶

🔎 SEE ALSO 🔎

The kernel file is ./drivers/i2c/i2c-core-base.c, and the whole friend group is right here:

• i2c_verify_client(9)
• i2c_adapter_lock_bus(9)
• i2c_adapter_trylock_bus(9)
• i2c_adapter_unlock_bus(9)
• i2c_new_client_device(9)
• i2c_unregister_device(9)
• i2c_find_device_by_fwnode(9)
• i2c_new_dummy_device(9)
• devm_i2c_new_dummy_device(9)
• i2c_new_ancillary_device(9)
• i2c_verify_adapter(9)
• i2c_handle_smbus_host_notify(9)
• i2c_add_adapter(9)
• i2c_del_adapter(9)
• devm_i2c_add_adapter(9)
• i2c_find_adapter_by_fwnode(9)
• i2c_get_adapter_by_fwnode(9)
• i2c_parse_fw_timings(9)
• i2c_del_driver(9)
• __i2c_transfer(9)
• i2c_transfer(9)
• i2c_transfer_buffer_flags(9)
• i2c_get_device_id(9)
• i2c_client_get_device_id(9)
• i2c_get_dma_safe_msg_buf(9)
• i2c_put_dma_safe_msg_buf(9)

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xoxo, the ./drivers/i2c girlies — October 2026 💋💖