nvme: document nvme controller states

We are starting to see some non-trivial states
so lets start documenting them.
Signed-off-by: NSagi Grimberg <sagi@grimberg.me>
Signed-off-by: NChristoph Hellwig <hch@lst.de>

drivers/nvme/host/nvme.h

@@ -181,6 +181,20 @@ static inline u16 nvme_req_qid(struct request *req)
  */
 #define NVME_QUIRK_DELAY_AMOUNT		2300
 
+/*
+ * enum nvme_ctrl_state: Controller state
+ *
+ * @NVME_CTRL_NEW:		New controller just allocated, initial state
+ * @NVME_CTRL_LIVE:		Controller is connected and I/O capable
+ * @NVME_CTRL_RESETTING:	Controller is resetting (or scheduled reset)
+ * @NVME_CTRL_CONNECTING:	Controller is disconnected, now connecting the
+ *				transport
+ * @NVME_CTRL_DELETING:		Controller is deleting (or scheduled deletion)
+ * @NVME_CTRL_DEAD:		Controller is non-present/unresponsive during
+ *				shutdown or removal. In this case we forcibly
+ *				kill all inflight I/O as they have no chance to
+ *				complete
+ */
 enum nvme_ctrl_state {
 	NVME_CTRL_NEW,
 	NVME_CTRL_LIVE,