i2c_txn_tag_t
i2c_txn_tag_t txn_tag;
extern i2c_txn_t *i2c_txn_alloc(i2c_ctrl_t *, i2c_txn_tag_t, const void *);
i2c_client_bus_lock(i2c_ctrl_t *ctrl, i2c_txn_tag_t tag, const void *arg,
i2c_txn_alloc(i2c_ctrl_t *ctrl, i2c_txn_tag_t tag, const void *debug)
i2c_user_acquire(i2c_user_t *user, i2c_txn_tag_t tag, bool block, bool nexus,