+ * @pending: True for xfers added to @pending_xfers hashtable
+ * @node: An hlist_node reference used to store this xfer, alternatively, on
+ * the free list @free_xfers or in the @pending_xfers hashtable
+ * @users: A refcount to track the active users for this xfer.
+ * This is meant to protect against the possibility that, when a command
+ * transaction times out concurrently with the reception of a valid
+ * response message, the xfer could be finally put on the TX path, and
+ * so vanish, while on the RX path scmi_rx_callback() is still
+ * processing it: in such a case this refcounting will ensure that, even
+ * though the timed-out transaction will anyway cause the command
+ * request to be reported as failed by time-out, the underlying xfer
+ * cannot be discarded and possibly reused until the last one user on
+ * the RX path has released it.
+ * @busy: An atomic flag to ensure exclusive write access to this xfer
+ * @state: The current state of this transfer, with states transitions deemed
+ * valid being:
+ * - SCMI_XFER_SENT_OK -> SCMI_XFER_RESP_OK [ -> SCMI_XFER_DRESP_OK ]
+ * - SCMI_XFER_SENT_OK -> SCMI_XFER_DRESP_OK
+ * (Missing synchronous response is assumed OK and ignored)
+ * @lock: A spinlock to protect state and busy fields.
+ * @priv: A pointer for transport private usage.