HIDI2C_LENGTH_LEN
size_t read_len = HIDI2C_LENGTH_LEN;
buf_len += data_len + HIDI2C_LENGTH_LEN;
put_unaligned_le16(data_len + HIDI2C_LENGTH_LEN, write_buf + offset);
offset += HIDI2C_LENGTH_LEN;
#define HIDI2C_PACKET_LEN(data_len) ((data_len) + HIDI2C_LENGTH_LEN)
#define HIDI2C_DATA_LEN(pkt_len) ((pkt_len) - HIDI2C_LENGTH_LEN)