STRUCT I2C_ADAPTER_QUIRKS(9)

🌸 NAME 🌸

struct i2c_adapter_quirks — describe flaws of an i2c adapter. From the Kernel API Manual, bestie, and yes, this is the little struct that spills the tea on an adapter’s quirky limits. 💅

✨ SYNOPSIS ✨

       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 for the full story. ✨
• max_num_msgs — maximum number of messages per transfer. That’s the cap, no cap. 🎀
• max_write_len — maximum length of a write message. Keep it cute and within bounds. 💖
• max_read_len — maximum length of a read message. Same energy, different direction. 🦋
• max_comb_1st_msg_len — maximum length of the first msg in a combined message. Yes, “msg” is the word here. 🌸
• max_comb_2nd_msg_len — maximum length of the second msg in a combined message. The sequel has limits too. 💀

🔥 Description 🔥

Okay so, the 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. 🧚

🌈 SEE ALSO 🌈

• Kernel file ./include/linux/i2c.h
• 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_algorithm(9)
• struct i2c_lock_operations(9)
• struct i2c_timings(9)
• struct i2c_bus_recovery_info(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)

Bye bestie! 💖 Source/version/date tea: ./include/linux, dated October 2026, and the page is struct i2c_adapter_quirks(9). 🎀 👑