[RFC PATCH v1 2/7] nvmef: Add nvmef_req_hold_timeout_ms() to calculate kato request hold time

[Mohamed Khalfella <mkhalfella@purestorage.com>]

nvme request hold timeout is the time sufficient for target controller
to learn about loss of connectivity to initiator and quiesce inflight
nvme commands.

The timeout has two components:

- KATO timeout is the time sufficient for target to learn about the
  connection loss to the target. It depends on whether command based or
  traffic based keepalive is used. As per TP4129 the timeout is supposed
  to be 3 x KATO for traffic based keepalive and 2 * KATO for command
  based keepalive.

- CQT is the time needed by target controller to quiesce in flight nvme
  commands after the controller learns about connection loss.

Signed-off-by: Mohamed Khalfella <mkhalfella@purestorage.com>
---
 drivers/nvme/host/fabrics.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/nvme/host/fabrics.h b/drivers/nvme/host/fabrics.h
index 21d75dc4a3a0..483823d430d0 100644
--- a/drivers/nvme/host/fabrics.h
+++ b/drivers/nvme/host/fabrics.h
@@ -214,6 +214,13 @@ static inline unsigned int nvmf_nr_io_queues(struct nvmf_ctrl_options *opts)
 		min(opts->nr_poll_queues, num_online_cpus());
 }
 
+static inline unsigned int nvmef_req_hold_timeout_ms(struct nvme_ctrl *ctrl)
+{
+	if (ctrl->ctratt & NVME_CTRL_ATTR_TBKAS)
+		return 3 * ctrl->kato * 1000 + ctrl->cqt;
+	return 2 * ctrl->kato * 1000 + ctrl->cqt;
+}
+
 int nvmf_reg_read32(struct nvme_ctrl *ctrl, u32 off, u32 *val);
 int nvmf_reg_read64(struct nvme_ctrl *ctrl, u32 off, u64 *val);
 int nvmf_reg_write32(struct nvme_ctrl *ctrl, u32 off, u32 val);
-- 
2.48.1