nvme: Use non zero KATO for persistent discovery connections

The NVMe Base Specification 2.1 states that:

"""
A host requests an explicit persistent connection ... by specifying a
non-zero Keep Alive Timer value in the Connect command.
"""

As such if we are starting a persistent connection to a discovery
controller and the KATO is currently 0 we need to update KATO to a non
zero value to avoid continuous timeouts on the target.

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>

Author: alistair23

drivers/nvme/host/core.c

@@ -4991,8 +4991,14 @@ void nvme_start_ctrl(struct nvme_ctrl *ctrl)
 	 * checking that they started once before, hence are reconnecting back.
 	 */
 	if (test_bit(NVME_CTRL_STARTED_ONCE, &ctrl->flags) &&
-	    nvme_discovery_ctrl(ctrl))
+	    nvme_discovery_ctrl(ctrl)) {
+		if (!ctrl->kato) {
+			nvme_stop_keep_alive(ctrl);
+			ctrl->kato = NVME_DEFAULT_KATO;
+			nvme_start_keep_alive(ctrl);
+		}
 		nvme_change_uevent(ctrl, "NVME_EVENT=rediscover");
+	}
 
 	if (ctrl->queue_count > 1) {
 		nvme_queue_scan(ctrl);