linux-kernel - [PATCH] nvme: Use non zero KATO for persistent discovery connections

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Message-ID: <20250902035211.2953174-1-alistair.francis@wdc.com>
Date: Tue,  2 Sep 2025 13:52:11 +1000
From: alistair23@...il.com
To: kbusch@...nel.org,
	axboe@...nel.dk,
	hch@....de,
	sagi@...mberg.me,
	linux-nvme@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org,
	alistair23@...il.com,
	Alistair Francis <alistair.francis@....com>
Subject: [PATCH] nvme: Use non zero KATO for persistent discovery connections

From: Alistair Francis <alistair.francis@....com>

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@....com>
---
 drivers/nvme/host/core.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 812c1565114f..bb9685b67338 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -4986,8 +4986,14 @@ 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);
-- 
2.50.1