[PATCH v3 3/3] ethdev: document special cases of port start and stop

[Dariusz Sosnowski <dsosnowski@nvidia.com>]

This patch clarifies the handling of following cases
in the ethdev API docs:

- If rte_eth_dev_start() returns (-EAGAIN) for some port,
  it cannot be started right now and start operation
  must be retried.
- If rte_eth_dev_stop() returns (-EBUSY) for some port,
  it cannot be stopped in the current state.

When stopping the port in testpmd fails,
port's state is switched back to STARTED
to allow users to manually retry stopping the port.

No additional changes in testpmd are required to handle
failures to start the port.
If rte_eth_dev_start() fails, port's state is switched to STOPPED
and users are allowed to retry the operation.

Signed-off-by: Dariusz Sosnowski <dsosnowski@nvidia.com>
---
 app/test-pmd/testpmd.c  | 8 +++++++-
 lib/ethdev/rte_ethdev.h | 2 ++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/app/test-pmd/testpmd.c b/app/test-pmd/testpmd.c
index 4e25f77c6a..a0b4ede48b 100644
--- a/app/test-pmd/testpmd.c
+++ b/app/test-pmd/testpmd.c
@@ -3182,6 +3182,7 @@ stop_port(portid_t pid)
 	int need_check_link_status = 0;
 	portid_t peer_pl[RTE_MAX_ETHPORTS];
 	int peer_pi;
+	int ret;
 
 	if (port_id_is_invalid(pid, ENABLED_WARN))
 		return;
@@ -3231,9 +3232,14 @@ stop_port(portid_t pid)
 		if (port->flow_list)
 			port_flow_flush(pi);
 
-		if (eth_dev_stop_mp(pi) != 0)
+		ret = eth_dev_stop_mp(pi);
+		if (ret != 0) {
 			RTE_LOG(ERR, EAL, "rte_eth_dev_stop failed for port %u\n",
 				pi);
+			/* Allow to retry stopping the port. */
+			port->port_status = RTE_PORT_STARTED;
+			continue;
+		}
 
 		if (port->port_status == RTE_PORT_HANDLING)
 			port->port_status = RTE_PORT_STOPPED;
diff --git a/lib/ethdev/rte_ethdev.h b/lib/ethdev/rte_ethdev.h
index 13fe73d5a3..c129ca1eaf 100644
--- a/lib/ethdev/rte_ethdev.h
+++ b/lib/ethdev/rte_ethdev.h
@@ -2705,6 +2705,7 @@ int rte_eth_dev_tx_queue_stop(uint16_t port_id, uint16_t tx_queue_id);
  *   The port identifier of the Ethernet device.
  * @return
  *   - 0: Success, Ethernet device started.
+ *   - -EAGAIN: If start operation must be retried.
  *   - <0: Error code of the driver device start function.
  */
 int rte_eth_dev_start(uint16_t port_id);
@@ -2717,6 +2718,7 @@ int rte_eth_dev_start(uint16_t port_id);
  *   The port identifier of the Ethernet device.
  * @return
  *   - 0: Success, Ethernet device stopped.
+ *   - -EBUSY: If stopping the port is not allowed in current state.
  *   - <0: Error code of the driver device stop function.
  */
 int rte_eth_dev_stop(uint16_t port_id);
-- 
2.25.1