mlxsw: spectrum_span: Only update mirroring agents if present

In order not to needlessly schedule the work item that updates the
mirroring agents, only schedule it if there are any mirroring agents
present.

This is done by adding an atomic counter that counts the active
mirroring agents.

It is incremented / decremented whenever a mirroring agent is created /
destroyed. It is read before scheduling the work item and in the
devlink-resource occupancy callback.
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlxsw/spectrum_span.c

@@ -19,6 +19,7 @@
 struct mlxsw_sp_span {
 	struct work_struct work;
 	struct mlxsw_sp *mlxsw_sp;
+	atomic_t active_entries_count;
 	int entries_count;
 	struct mlxsw_sp_span_entry entries[0];
 };
@@ -28,15 +29,8 @@ static void mlxsw_sp_span_respin_work(struct work_struct *work);
 static u64 mlxsw_sp_span_occ_get(void *priv)
 {
 	const struct mlxsw_sp *mlxsw_sp = priv;
-	u64 occ = 0;
-	int i;
-
-	for (i = 0; i < mlxsw_sp->span->entries_count; i++) {
-		if (mlxsw_sp->span->entries[i].ref_count)
-			occ++;
-	}
 
-	return occ;
+	return atomic_read(&mlxsw_sp->span->active_entries_count);
 }
 
 int mlxsw_sp_span_init(struct mlxsw_sp *mlxsw_sp)
@@ -53,6 +47,7 @@ int mlxsw_sp_span_init(struct mlxsw_sp *mlxsw_sp)
 	if (!span)
 		return -ENOMEM;
 	span->entries_count = entries_count;
+	atomic_set(&span->active_entries_count, 0);
 	span->mlxsw_sp = mlxsw_sp;
 	mlxsw_sp->span = span;
 
@@ -668,6 +663,7 @@ mlxsw_sp_span_entry_create(struct mlxsw_sp *mlxsw_sp,
 	if (!span_entry)
 		return NULL;
 
+	atomic_inc(&mlxsw_sp->span->active_entries_count);
 	span_entry->ops = ops;
 	span_entry->ref_count = 1;
 	span_entry->to_dev = to_dev;
@@ -676,9 +672,11 @@ mlxsw_sp_span_entry_create(struct mlxsw_sp *mlxsw_sp,
 	return span_entry;
 }
 
-static void mlxsw_sp_span_entry_destroy(struct mlxsw_sp_span_entry *span_entry)
+static void mlxsw_sp_span_entry_destroy(struct mlxsw_sp *mlxsw_sp,
+					struct mlxsw_sp_span_entry *span_entry)
 {
 	mlxsw_sp_span_entry_deconfigure(span_entry);
+	atomic_dec(&mlxsw_sp->span->active_entries_count);
 }
 
 struct mlxsw_sp_span_entry *
@@ -740,7 +738,7 @@ static int mlxsw_sp_span_entry_put(struct mlxsw_sp *mlxsw_sp,
 {
 	WARN_ON(!span_entry->ref_count);
 	if (--span_entry->ref_count == 0)
-		mlxsw_sp_span_entry_destroy(span_entry);
+		mlxsw_sp_span_entry_destroy(mlxsw_sp, span_entry);
 	return 0;
 }
 
@@ -1033,5 +1031,7 @@ static void mlxsw_sp_span_respin_work(struct work_struct *work)
 
 void mlxsw_sp_span_respin(struct mlxsw_sp *mlxsw_sp)
 {
+	if (atomic_read(&mlxsw_sp->span->active_entries_count) == 0)
+		return;
 	mlxsw_core_schedule_work(&mlxsw_sp->span->work);
 }