Subject: [PATCH v3 net-next 9/9] net: dsa: netc: implement dynamic FDB entry ageing

From: [email-masked]
Date: Fri, 5 Jun 2026 09:48:08 +0800

From: Wei Fang <[email-masked]>

The NETC switch does not age out dynamic FDB entries automatically.
Without software management, stale entries persist after topology
changes and cause incorrect forwarding.

Add a delayed work that periodically removes entries that have not been
refreshed within the specified cycles. The effective ageing time is:

  ageing_time = fdbt_ageing_delay * 100

Default values are 3s interval and 100 cycles (300s total), matching
the IEEE 802.1Q default ageing time. The work starts when the first
port joins a bridge (tracked via br_cnt) and is cancelled when the
last port leaves. All FDB operations are serialized under fdbt_lock.

Implement .set_ageing_time() to allow the bridge layer to reconfigure
ageing parameters on demand.

Signed-off-by: Wei Fang <[email-masked]>
---
 drivers/net/dsa/netc/netc_main.c   | 67 ++++++++++++++++++++++++++++++
 drivers/net/dsa/netc/netc_switch.h |  7 ++++
 2 files changed, 74 insertions(+)

diff --git a/drivers/net/dsa/netc/netc_main.c b/drivers/net/dsa/netc/netc_main.c
index b61152c16e7b..a8e036a7046c 100644
--- a/drivers/net/dsa/netc/netc_main.c
+++ b/drivers/net/dsa/netc/netc_main.c
@@ -447,6 +447,25 @@ static void netc_free_ntmp_user(struct netc_switch *priv)
 	netc_free_ntmp_bitmaps(priv);
 }
 
+static void netc_clean_fdbt_ageing_entries(struct work_struct *work)
+{
+	struct delayed_work *dwork = to_delayed_work(work);
+	struct netc_switch *priv;
+
+	priv = container_of(dwork, struct netc_switch, fdbt_ageing_work);
+
+	/* Update the activity element in FDB table */
+	mutex_lock(&priv->fdbt_lock);
+	ntmp_fdbt_update_activity_element(&priv->ntmp);
+	/* Delete the ageing entries after the activity element is updated */
+	ntmp_fdbt_delete_ageing_entries(&priv->ntmp, NETC_FDBT_AGEING_THRESH);
+	mutex_unlock(&priv->fdbt_lock);
+
+	if (atomic_read(&priv->br_cnt))
+		schedule_delayed_work(&priv->fdbt_ageing_work,
+				      READ_ONCE(priv->fdbt_ageing_delay));
+}
+
 static void netc_switch_dos_default_config(struct netc_switch *priv)
 {
 	struct netc_switch_regs *regs = &priv->regs;
@@ -872,6 +891,10 @@ static int netc_setup(struct dsa_switch *ds)
 
 	INIT_HLIST_HEAD(&priv->fdb_list);
 	mutex_init(&priv->fdbt_lock);
+	priv->fdbt_ageing_delay = NETC_FDBT_AGEING_DELAY;
+	atomic_set(&priv->br_cnt, 0);
+	INIT_DELAYED_WORK(&priv->fdbt_ageing_work,
+			  netc_clean_fdbt_ageing_entries);
 	INIT_HLIST_HEAD(&priv->vlan_list);
 	mutex_init(&priv->vft_lock);
 
@@ -936,6 +959,7 @@ static void netc_teardown(struct dsa_switch *ds)
 {
 	struct netc_switch *priv = ds->priv;
 
+	disable_delayed_work_sync(&priv->fdbt_ageing_work);
 	netc_destroy_all_lists(priv);
 	netc_free_host_flood_rules(priv);
 	netc_free_ntmp_user(priv);
@@ -1961,6 +1985,7 @@ static int netc_port_bridge_join(struct dsa_switch *ds, int port,
 				 struct netlink_ext_ack *extack)
 {
 	struct netc_port *np = NETC_PORT(ds, port);
+	struct netc_switch *priv = ds->priv;
 	u16 vlan_unaware_pvid;
 	int err;
 
@@ -1988,6 +2013,10 @@ static int netc_port_bridge_join(struct dsa_switch *ds, int port,
 out:
 	netc_port_remove_host_flood(np, np->host_flood);
 
+	if (atomic_inc_return(&priv->br_cnt) == 1)
+		schedule_delayed_work(&priv->fdbt_ageing_work,
+				      READ_ONCE(priv->fdbt_ageing_delay));
+
 	return 0;
 
 disable_mlo:
@@ -2014,6 +2043,7 @@ static void netc_port_bridge_leave(struct dsa_switch *ds, int port,
 {
 	struct netc_port *np = NETC_PORT(ds, port);
 	struct net_device *ndev = np->dp->user;
+	struct netc_switch *priv = ds->priv;
 	u16 vlan_unaware_pvid;
 	bool mc, uc;
 
@@ -2021,6 +2051,9 @@ static void netc_port_bridge_leave(struct dsa_switch *ds, int port,
 	netc_port_set_pvid(np, NETC_STANDALONE_PVID);
 	np->pvid = NETC_STANDALONE_PVID;
 
+	if (atomic_dec_and_test(&priv->br_cnt))
+		cancel_delayed_work_sync(&priv->fdbt_ageing_work);
+
 	netc_port_remove_dynamic_entries(np);
 	uc = ndev->flags & IFF_PROMISC;
 	mc = ndev->flags & (IFF_PROMISC | IFF_ALLMULTI);
@@ -2041,6 +2074,37 @@ static void netc_port_bridge_leave(struct dsa_switch *ds, int port,
 	netc_port_del_vlan_entry(np, vlan_unaware_pvid);
 }
 
+static int netc_set_ageing_time(struct dsa_switch *ds, unsigned int msecs)
+{
+	struct netc_switch *priv = ds->priv;
+	unsigned long delay_jiffies;
+
+	/* The dynamic FDB entry is deleted when its activity counter reaches
+	 * NETC_FDBT_AGEING_THRESH (100). Each delayed_work tick increments
+	 * the counter by 1 if the entry is inactive.
+	 *
+	 * Therefore:
+	 *   msecs (ms)    = NETC_FDBT_AGEING_THRESH * delay_ms (ms)
+	 *   delay_ms      = msecs / NETC_FDBT_AGEING_THRESH
+	 *   delay_jiffies = (delay_ms / 1000) * HZ
+	 *                 = (msecs * HZ) / (1000 * NETC_FDBT_AGEING_THRESH)
+	 *
+	 * Use DIV_ROUND_CLOSEST_ULL to perform a single nearest-jiffy
+	 * rounding, avoiding the two-step rounding error of the intermediate
+	 * delay_ms approach.
+	 *   Maximum error = +/-0.5 jiffy * 100 = +/-50000/HZ ms.
+	 */
+	delay_jiffies = DIV_ROUND_CLOSEST_ULL((u64)msecs * HZ,
+					      1000 * NETC_FDBT_AGEING_THRESH);
+	WRITE_ONCE(priv->fdbt_ageing_delay, delay_jiffies);
+
+	if (atomic_read(&priv->br_cnt))
+		mod_delayed_work(system_percpu_wq, &priv->fdbt_ageing_work,
+				 READ_ONCE(priv->fdbt_ageing_delay));
+
+	return 0;
+}
+
 static void netc_port_fast_age(struct dsa_switch *ds, int port)
 {
 	struct netc_port *np = NETC_PORT(ds, port);
@@ -2332,6 +2396,7 @@ static const struct dsa_switch_ops netc_switch_ops = {
 	.port_vlan_del			= netc_port_vlan_del,
 	.port_bridge_join		= netc_port_bridge_join,
 	.port_bridge_leave		= netc_port_bridge_leave,
+	.set_ageing_time		= netc_set_ageing_time,
 	.port_fast_age			= netc_port_fast_age,
 	.get_pause_stats		= netc_port_get_pause_stats,
 	.get_rmon_stats			= netc_port_get_rmon_stats,
@@ -2381,6 +2446,8 @@ static int netc_switch_probe(struct pci_dev *pdev,
 	ds->phylink_mac_ops = &netc_phylink_mac_ops;
 	ds->fdb_isolation = true;
 	ds->max_num_bridges = priv->info->num_ports - 1;
+	ds->ageing_time_min = 1000;
+	ds->ageing_time_max = U32_MAX;
 	ds->priv = priv;
 	priv->ds = ds;
 
diff --git a/drivers/net/dsa/netc/netc_switch.h b/drivers/net/dsa/netc/netc_switch.h
index 982c8d3a3fbf..305f2a92e2f9 100644
--- a/drivers/net/dsa/netc/netc_switch.h
+++ b/drivers/net/dsa/netc/netc_switch.h
@@ -50,6 +50,9 @@
 /* PAUSE refresh threshold: send refresh when timer reaches this value */
 #define NETC_PAUSE_THRESH		0x7FFF
 
+#define NETC_FDBT_AGEING_DELAY		(3 * HZ)
+#define NETC_FDBT_AGEING_THRESH		100
+
 struct netc_switch;
 
 struct netc_switch_info {
@@ -124,6 +127,10 @@ struct netc_switch {
 	struct ntmp_user ntmp;
 	struct hlist_head fdb_list;
 	struct mutex fdbt_lock; /* FDB table lock */
+	struct delayed_work fdbt_ageing_work;
+	/* (fdbt_ageing_delay * NETC_FDBT_AGEING_THRESH) is ageing time */
+	unsigned long fdbt_ageing_delay;
+	atomic_t br_cnt;
 	struct hlist_head vlan_list;
 	struct mutex vft_lock; /* VLAN filter table lock */
 
-- 
2.34.1