struct i2c_adapter_quirks — describe flaws of an i2c adapter
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;
}; see I2C_AQ_* for possible flags and read below
maximum number of messages per transfer
maximum length of a write message
maximum length of a read message
maximum length of the first msg in a combined message
maximum length of the second msg in a combined message
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.