[PATCH net-next 04/15] net/mlx5: SD, make primary/secondary role determination more robust

[Tariq Toukan <tariqt@nvidia.com>]

From: Shay Drory <shayd@nvidia.com>

Refactor SD group registration to use devcom event-driven role
determination to ensure SD is marked as ready only after roles are fully
assigned and the group state is consistent, making outside accessors,
which will be added in downstream patches, safe to use without races.

The devcom events:
- SD_PRIMARY_SET event: each device compares bus numbers with peers
  to determine which should be primary
- SD_SECONDARIES_SET event: secondaries register themselves with the
  elected primary device

Signed-off-by: Shay Drory <shayd@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
---
 .../net/ethernet/mellanox/mlx5/core/lib/sd.c  | 137 +++++++++++++-----
 1 file changed, 102 insertions(+), 35 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/lib/sd.c b/drivers/net/ethernet/mellanox/mlx5/core/lib/sd.c
index 25286ecd724e..41979bf6a615 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/lib/sd.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/lib/sd.c
@@ -26,6 +26,8 @@ struct mlx5_sd {
 		struct { /* primary */
 			struct mlx5_core_dev *secondaries[MLX5_SD_MAX_GROUP_SZ - 1];
 			struct mlx5_flow_table *tx_ft;
+			/* Next index for secondary registration */
+			u8 next_secondary_idx;
 		};
 		struct { /* secondary */
 			struct mlx5_core_dev *primary_dev;
@@ -374,62 +376,125 @@ static void sd_lag_cleanup(struct mlx5_core_dev *dev)
 	mutex_unlock(&ldev->lock);
 }
 
+enum {
+	SD_PRIMARY_SET,
+	SD_SECONDARIES_SET,
+};
+
+static void sd_handle_primary_set(struct mlx5_core_dev *dev,
+				  struct mlx5_core_dev *peer)
+{
+	struct mlx5_sd *peer_sd = mlx5_get_sd(peer);
+	struct mlx5_sd *sd = mlx5_get_sd(dev);
+	struct mlx5_core_dev *candidate;
+	struct mlx5_sd *candidate_sd;
+
+	/* Peer is the device that being sent to all the other devices in the
+	 * group. Hence, use peer to get the candidate device.
+	 */
+	candidate = peer_sd->primary ? peer : peer_sd->primary_dev;
+
+	if (dev->pdev->bus->number >= candidate->pdev->bus->number)
+		return;
+
+	candidate_sd = mlx5_get_sd(candidate);
+
+	sd->primary = true;
+	candidate_sd->primary = false;
+	candidate_sd->primary_dev = dev;
+	peer_sd->primary = false;
+	peer_sd->primary_dev = dev;
+}
+
+static void sd_handle_secondaries_set(struct mlx5_core_dev *dev,
+				      struct mlx5_core_dev *peer)
+{
+	struct mlx5_sd *peer_sd = mlx5_get_sd(peer);
+	struct mlx5_sd *sd = mlx5_get_sd(dev);
+	u8 idx;
+
+	/* Primary has nothing to register with itself. */
+	if (sd->primary)
+		return;
+
+	/* dev is a secondary device, peer is the primary device.
+	 * Secondary registers itself with the primary.
+	 */
+	idx = peer_sd->next_secondary_idx++;
+	peer_sd->secondaries[idx] = dev;
+	sd->primary_dev = peer;
+}
+
+static int mlx5_sd_devcom_event(int event, void *my_data, void *event_data)
+{
+	struct mlx5_core_dev *peer = event_data;
+	struct mlx5_core_dev *dev = my_data;
+
+	switch (event) {
+	case SD_PRIMARY_SET:
+		sd_handle_primary_set(dev, peer);
+		break;
+	case SD_SECONDARIES_SET:
+		sd_handle_secondaries_set(dev, peer);
+		break;
+	}
+
+	return 0;
+}
+
 static int sd_register(struct mlx5_core_dev *dev)
 {
-	struct mlx5_devcom_comp_dev *devcom, *pos;
 	struct mlx5_devcom_match_attr attr = {};
-	struct mlx5_core_dev *peer, *primary;
-	struct mlx5_sd *sd, *primary_sd;
-	int err, i;
+	struct mlx5_devcom_comp_dev *devcom;
+	struct mlx5_core_dev *primary;
+	struct mlx5_sd *sd;
+	int err;
 
 	sd = mlx5_get_sd(dev);
 	attr.key.val = sd->group_id;
 	attr.flags = MLX5_DEVCOM_MATCH_FLAGS_NS;
 	attr.net = mlx5_core_net(dev);
-	devcom = mlx5_devcom_register_component(dev->priv.devc, MLX5_DEVCOM_SD_GROUP,
-						&attr, NULL, dev);
+	devcom = mlx5_devcom_register_component(dev->priv.devc,
+						MLX5_DEVCOM_SD_GROUP,
+						&attr, mlx5_sd_devcom_event,
+						dev);
 	if (!devcom)
 		return -EINVAL;
 
 	sd->devcom = devcom;
 
-	if (mlx5_devcom_comp_get_size(devcom) != sd->host_buses)
-		return 0;
-
 	mlx5_devcom_comp_lock(devcom);
-	mlx5_devcom_comp_set_ready(devcom, true);
-	mlx5_devcom_comp_unlock(devcom);
+	if (mlx5_devcom_comp_get_size(devcom) != sd->host_buses ||
+	    mlx5_devcom_comp_is_ready(devcom))
+		goto out;
 
-	if (!mlx5_devcom_for_each_peer_begin(devcom)) {
-		err = -ENODEV;
+	/* Send SD_PRIMARY_SET event with this device.
+	 * All peers will receive this event and compare to this device.
+	 * The one with lowest bus number will be marked as primary.
+	 */
+	sd->primary = true;
+	err = mlx5_devcom_locked_send_event(devcom, SD_PRIMARY_SET,
+					    SD_PRIMARY_SET, dev);
+	if (err)
 		goto err_devcom_unreg;
-	}
-
-	primary = dev;
-	mlx5_devcom_for_each_peer_entry(devcom, peer, pos)
-		if (peer->pdev->bus->number < primary->pdev->bus->number)
-			primary = peer;
 
-	primary_sd = mlx5_get_sd(primary);
-	primary_sd->primary = true;
-	i = 0;
-	/* loop the secondaries */
-	mlx5_devcom_for_each_peer_entry(primary_sd->devcom, peer, pos) {
-		struct mlx5_sd *peer_sd = mlx5_get_sd(peer);
-
-		primary_sd->secondaries[i++] = peer;
-		peer_sd->primary = false;
-		peer_sd->primary_dev = primary;
-	}
+	/* Broadcast SD_SECONDARIES_SET. Each non-sender peer's handler runs;
+	 * the primary's handler returns early so only secondaries register.
+	 */
+	primary = sd->primary ? dev : sd->primary_dev;
+	if (!sd->primary)
+		sd_handle_secondaries_set(dev, primary);
+	mlx5_devcom_locked_send_event(devcom, SD_SECONDARIES_SET,
+				      DEVCOM_CANT_FAIL, primary);
 
-	mlx5_devcom_for_each_peer_end(devcom);
+	mlx5_devcom_comp_set_ready(devcom, true);
+out:
+	mlx5_devcom_comp_unlock(devcom);
 	return 0;
 
 err_devcom_unreg:
-	mlx5_devcom_comp_lock(sd->devcom);
-	mlx5_devcom_comp_set_ready(sd->devcom, false);
-	mlx5_devcom_comp_unlock(sd->devcom);
-	mlx5_devcom_unregister_component(sd->devcom);
+	mlx5_devcom_comp_unlock(devcom);
+	mlx5_devcom_unregister_component(devcom);
 	return err;
 }
 
@@ -672,6 +737,7 @@ int mlx5_sd_init(struct mlx5_core_dev *dev)
 		peer_sd->primary_dev = NULL;
 	}
 	primary_sd->primary = false;
+	primary_sd->next_secondary_idx = 0;
 	mlx5_devcom_comp_set_ready(sd->devcom, false);
 	mlx5_devcom_comp_unlock(sd->devcom);
 	sd_unregister(dev);
@@ -719,6 +785,7 @@ void mlx5_sd_cleanup(struct mlx5_core_dev *dev)
 		peer_sd->primary_dev = NULL;
 	}
 	primary_sd->primary = false;
+	primary_sd->next_secondary_idx = 0;
 out_ready_false:
 	mlx5_devcom_comp_set_ready(sd->devcom, false);
 out_unlock:
-- 
2.44.0