[PATCH v2 08/10] ethdev: add getter for per-queue Tx rate limit

[Vincent Jardin]

The existing rte_eth_set_queue_rate_limit() API allows setting a
per-queue Tx rate but provides no way to read it back. Applications
such as grout are forced to maintain a shadow copy of the rate to
be able to report it.

Add rte_eth_get_queue_rate_limit() as the symmetric getter, following
the established DPDK pattern (e.g. rte_eth_dev_set_mtu/get_mtu,
rte_eth_dev_set_vlan_offload/get_vlan_offload).

This adds:
- eth_get_queue_rate_limit_t driver callback in ethdev_driver.h
- rte_eth_get_queue_rate_limit() public experimental API (26.07)
- mlx5 PMD implementation reading from the existing per-queue
  rate_mbps tracking field

Signed-off-by: Vincent Jardin <vjardin at free.fr>
---
 doc/guides/rel_notes/release_26_03.rst |  5 ++++
 drivers/net/mlx5/mlx5.c                |  2 ++
 drivers/net/mlx5/mlx5_tx.h             |  2 ++
 drivers/net/mlx5/mlx5_txq.c            | 34 ++++++++++++++++++++++++++
 lib/ethdev/ethdev_driver.h             |  7 ++++++
 lib/ethdev/rte_ethdev.c                | 28 +++++++++++++++++++++
 lib/ethdev/rte_ethdev.h                | 24 ++++++++++++++++++
 7 files changed, 102 insertions(+)

diff --git a/doc/guides/rel_notes/release_26_03.rst b/doc/guides/rel_notes/release_26_03.rst
index b4499ec066..5afb2fd6d9 100644
--- a/doc/guides/rel_notes/release_26_03.rst
+++ b/doc/guides/rel_notes/release_26_03.rst
@@ -55,6 +55,11 @@ New Features
      Also, make sure to start the actual text at the margin.
      =======================================================
 
+* **Added per-queue Tx rate limit getter to ethdev.**
+
+  Added ``rte_eth_get_queue_rate_limit()`` experimental API
+  to retrieve the current per-queue Tx rate limit configured on a device.
+
 * **Added custom memory allocation hooks in ACL library.**
 
   Added a hook API mechanism
diff --git a/drivers/net/mlx5/mlx5.c b/drivers/net/mlx5/mlx5.c
index f399e0d5c9..6e21ed31f3 100644
--- a/drivers/net/mlx5/mlx5.c
+++ b/drivers/net/mlx5/mlx5.c
@@ -2721,6 +2721,7 @@ const struct eth_dev_ops mlx5_dev_ops = {
 	.rx_metadata_negotiate = mlx5_flow_rx_metadata_negotiate,
 	.get_restore_flags = mlx5_get_restore_flags,
 	.set_queue_rate_limit = mlx5_set_queue_rate_limit,
+	.get_queue_rate_limit = mlx5_get_queue_rate_limit,
 };
 
 /* Available operations from secondary process. */
@@ -2815,6 +2816,7 @@ const struct eth_dev_ops mlx5_dev_ops_isolate = {
 	.map_aggr_tx_affinity = mlx5_map_aggr_tx_affinity,
 	.get_restore_flags = mlx5_get_restore_flags,
 	.set_queue_rate_limit = mlx5_set_queue_rate_limit,
+	.get_queue_rate_limit = mlx5_get_queue_rate_limit,
 };
 
 /**
diff --git a/drivers/net/mlx5/mlx5_tx.h b/drivers/net/mlx5/mlx5_tx.h
index 3a37f5bb4d..46e199d93e 100644
--- a/drivers/net/mlx5/mlx5_tx.h
+++ b/drivers/net/mlx5/mlx5_tx.h
@@ -224,6 +224,8 @@ int mlx5_txq_releasable(struct rte_eth_dev *dev, uint16_t idx);
 int mlx5_txq_verify(struct rte_eth_dev *dev);
 int mlx5_set_queue_rate_limit(struct rte_eth_dev *dev, uint16_t queue_idx,
 			      uint32_t tx_rate);
+int mlx5_get_queue_rate_limit(struct rte_eth_dev *dev, uint16_t queue_idx,
+			      uint32_t *tx_rate);
 int mlx5_txq_get_sqn(struct mlx5_txq_ctrl *txq);
 void mlx5_txq_alloc_elts(struct mlx5_txq_ctrl *txq_ctrl);
 void mlx5_txq_free_elts(struct mlx5_txq_ctrl *txq_ctrl);
diff --git a/drivers/net/mlx5/mlx5_txq.c b/drivers/net/mlx5/mlx5_txq.c
index 155d544434..d5dab4f14a 100644
--- a/drivers/net/mlx5/mlx5_txq.c
+++ b/drivers/net/mlx5/mlx5_txq.c
@@ -1479,6 +1479,40 @@ mlx5_set_queue_rate_limit(struct rte_eth_dev *dev, uint16_t queue_idx,
 	return 0;
 }
 
+/**
+ * Get per-queue packet pacing rate limit.
+ *
+ * @param dev
+ *   Pointer to Ethernet device.
+ * @param queue_idx
+ *   TX queue index.
+ * @param[out] tx_rate
+ *   Pointer to store the TX rate in Mbps, 0 if rate limiting is disabled.
+ *
+ * @return
+ *   0 on success, a negative errno value otherwise and rte_errno is set.
+ */
+int
+mlx5_get_queue_rate_limit(struct rte_eth_dev *dev, uint16_t queue_idx,
+			  uint32_t *tx_rate)
+{
+	struct mlx5_priv *priv = dev->data->dev_private;
+	struct mlx5_txq_ctrl *txq_ctrl;
+
+	if (queue_idx >= dev->data->nb_tx_queues) {
+		rte_errno = EINVAL;
+		return -rte_errno;
+	}
+	if (priv->txqs == NULL || (*priv->txqs)[queue_idx] == NULL) {
+		rte_errno = EINVAL;
+		return -rte_errno;
+	}
+	txq_ctrl = container_of((*priv->txqs)[queue_idx],
+				struct mlx5_txq_ctrl, txq);
+	*tx_rate = txq_ctrl->rl.rate_mbps;
+	return 0;
+}
+
 /**
  * Verify if the queue can be released.
  *
diff --git a/lib/ethdev/ethdev_driver.h b/lib/ethdev/ethdev_driver.h
index 1255cd6f2c..0f336f9567 100644
--- a/lib/ethdev/ethdev_driver.h
+++ b/lib/ethdev/ethdev_driver.h
@@ -762,6 +762,11 @@ typedef int (*eth_set_queue_rate_limit_t)(struct rte_eth_dev *dev,
 				uint16_t queue_idx,
 				uint32_t tx_rate);
 
+/** @internal Get queue Tx rate. */
+typedef int (*eth_get_queue_rate_limit_t)(struct rte_eth_dev *dev,
+				uint16_t queue_idx,
+				uint32_t *tx_rate);
+
 /** @internal Add tunneling UDP port. */
 typedef int (*eth_udp_tunnel_port_add_t)(struct rte_eth_dev *dev,
 					 struct rte_eth_udp_tunnel *tunnel_udp);
@@ -1522,6 +1527,8 @@ struct eth_dev_ops {
 
 	/** Set queue rate limit */
 	eth_set_queue_rate_limit_t set_queue_rate_limit;
+	/** Get queue rate limit */
+	eth_get_queue_rate_limit_t get_queue_rate_limit;
 
 	/** Configure RSS hash protocols and hashing key */
 	rss_hash_update_t          rss_hash_update;
diff --git a/lib/ethdev/rte_ethdev.c b/lib/ethdev/rte_ethdev.c
index 2edc7a362e..c6ad399033 100644
--- a/lib/ethdev/rte_ethdev.c
+++ b/lib/ethdev/rte_ethdev.c
@@ -5694,6 +5694,34 @@ int rte_eth_set_queue_rate_limit(uint16_t port_id, uint16_t queue_idx,
 	return ret;
 }
 
+RTE_EXPORT_EXPERIMENTAL_SYMBOL(rte_eth_get_queue_rate_limit, 26.07)
+int rte_eth_get_queue_rate_limit(uint16_t port_id, uint16_t queue_idx,
+					uint32_t *tx_rate)
+{
+	struct rte_eth_dev *dev;
+
+	RTE_ETH_VALID_PORTID_OR_ERR_RET(port_id, -ENODEV);
+	dev = &rte_eth_devices[port_id];
+
+	if (tx_rate == NULL) {
+		RTE_ETHDEV_LOG_LINE(ERR,
+			"Get queue rate limit:port %u: NULL tx_rate pointer",
+			port_id);
+		return -EINVAL;
+	}
+
+	if (queue_idx >= dev->data->nb_tx_queues) {
+		RTE_ETHDEV_LOG_LINE(ERR,
+			"Get queue rate limit:port %u: invalid queue ID=%u",
+			port_id, queue_idx);
+		return -EINVAL;
+	}
+
+	if (dev->dev_ops->get_queue_rate_limit == NULL)
+		return -ENOTSUP;
+	return eth_err(port_id, dev->dev_ops->get_queue_rate_limit(dev, queue_idx, tx_rate));
+}
+
 RTE_EXPORT_EXPERIMENTAL_SYMBOL(rte_eth_rx_avail_thresh_set, 22.07)
 int rte_eth_rx_avail_thresh_set(uint16_t port_id, uint16_t queue_id,
 			       uint8_t avail_thresh)
diff --git a/lib/ethdev/rte_ethdev.h b/lib/ethdev/rte_ethdev.h
index 0d8e2d0236..e525217b77 100644
--- a/lib/ethdev/rte_ethdev.h
+++ b/lib/ethdev/rte_ethdev.h
@@ -4817,6 +4817,30 @@ int rte_eth_dev_uc_all_hash_table_set(uint16_t port_id, uint8_t on);
 int rte_eth_set_queue_rate_limit(uint16_t port_id, uint16_t queue_idx,
 			uint32_t tx_rate);
 
+/**
+ * @warning
+ * @b EXPERIMENTAL: this API may change, or be removed, without prior notice.
+ *
+ * Get the rate limitation for a queue on an Ethernet device.
+ *
+ * @param port_id
+ *   The port identifier of the Ethernet device.
+ * @param queue_idx
+ *   The queue ID.
+ * @param[out] tx_rate
+ *   A pointer to retrieve the Tx rate in Mbps.
+ *   0 means rate limiting is disabled.
+ * @return
+ *   - (0) if successful.
+ *   - (-ENOTSUP) if hardware doesn't support this feature.
+ *   - (-ENODEV) if *port_id* invalid.
+ *   - (-EIO) if device is removed.
+ *   - (-EINVAL) if bad parameter.
+ */
+__rte_experimental
+int rte_eth_get_queue_rate_limit(uint16_t port_id, uint16_t queue_idx,
+			uint32_t *tx_rate);
+
 /**
  * Configuration of Receive Side Scaling hash computation of Ethernet device.
  *
-- 
2.43.0