[PATCH net-next 2/2] net: phy: phy_link_topology: Lazy-initialize the link topology

[Maxime Chevallier <maxime.chevallier@bootlin.com>]

Having the net_device's init path for the link_topology depend on
IS_REACHABLE(PHYLIB)-protected helpers triggers errors when modules are being
built with phylib as a module as-well, as they expect netdev->link_topo
to be initialized.

Move the link_topo initialization at the first PHY insertion, which will
both improve the memory usage, and make the behaviour more predicatble
and robust.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Fixes: 6916e461e793 ("net: phy: Introduce ethernet link topology representation")
Closes: https://lore.kernel.org/netdev/2e11b89d-100f-49e7-9c9a-834cc0b82f97@gmail.com/
Closes: https://lore.kernel.org/netdev/20240409201553.GA4124869@dev-arch.thelio-3990X/
---
 drivers/net/phy/phy_link_topology.c    | 31 ++++++---------------
 include/linux/netdevice.h              |  2 ++
 include/linux/phy_link_topology.h      | 23 ++++++++--------
 include/linux/phy_link_topology_core.h | 23 +++-------------
 net/core/dev.c                         | 38 ++++++++++++++++++++++----
 5 files changed, 58 insertions(+), 59 deletions(-)

diff --git a/drivers/net/phy/phy_link_topology.c b/drivers/net/phy/phy_link_topology.c
index 0e36bd7c15dc..b1aba9313e73 100644
--- a/drivers/net/phy/phy_link_topology.c
+++ b/drivers/net/phy/phy_link_topology.c
@@ -12,29 +12,6 @@
 #include <linux/rtnetlink.h>
 #include <linux/xarray.h>
 
-struct phy_link_topology *phy_link_topo_create(struct net_device *dev)
-{
-	struct phy_link_topology *topo;
-
-	topo = kzalloc(sizeof(*topo), GFP_KERNEL);
-	if (!topo)
-		return ERR_PTR(-ENOMEM);
-
-	xa_init_flags(&topo->phys, XA_FLAGS_ALLOC1);
-	topo->next_phy_index = 1;
-
-	return topo;
-}
-
-void phy_link_topo_destroy(struct phy_link_topology *topo)
-{
-	if (!topo)
-		return;
-
-	xa_destroy(&topo->phys);
-	kfree(topo);
-}
-
 int phy_link_topo_add_phy(struct net_device *dev,
 			  struct phy_device *phy,
 			  enum phy_upstream upt, void *upstream)
@@ -43,6 +20,14 @@ int phy_link_topo_add_phy(struct net_device *dev,
 	struct phy_device_node *pdn;
 	int ret;
 
+	if (!topo) {
+		ret = netdev_alloc_phy_link_topology(dev);
+		if (ret)
+			return ret;
+
+		topo = dev->link_topo;
+	}
+
 	pdn = kzalloc(sizeof(*pdn), GFP_KERNEL);
 	if (!pdn)
 		return -ENOMEM;
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index cf261fb89d73..25a0a77cfadc 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -4569,6 +4569,8 @@ void __hw_addr_unsync_dev(struct netdev_hw_addr_list *list,
 					const unsigned char *));
 void __hw_addr_init(struct netdev_hw_addr_list *list);
 
+int netdev_alloc_phy_link_topology(struct net_device *dev);
+
 /* Functions used for device addresses handling */
 void dev_addr_mod(struct net_device *dev, unsigned int offset,
 		  const void *addr, size_t len);
diff --git a/include/linux/phy_link_topology.h b/include/linux/phy_link_topology.h
index 166a01710aa2..3501f9a9e932 100644
--- a/include/linux/phy_link_topology.h
+++ b/include/linux/phy_link_topology.h
@@ -32,10 +32,12 @@ struct phy_device_node {
 	struct phy_device *phy;
 };
 
-struct phy_link_topology {
-	struct xarray phys;
-	u32 next_phy_index;
-};
+#if IS_ENABLED(CONFIG_PHYLIB)
+int phy_link_topo_add_phy(struct net_device *dev,
+			  struct phy_device *phy,
+			  enum phy_upstream upt, void *upstream);
+
+void phy_link_topo_del_phy(struct net_device *dev, struct phy_device *phy);
 
 static inline struct phy_device
 *phy_link_topo_get_phy(struct net_device *dev, u32 phyindex)
@@ -53,13 +55,6 @@ static inline struct phy_device
 	return NULL;
 }
 
-#if IS_REACHABLE(CONFIG_PHYLIB)
-int phy_link_topo_add_phy(struct net_device *dev,
-			  struct phy_device *phy,
-			  enum phy_upstream upt, void *upstream);
-
-void phy_link_topo_del_phy(struct net_device *dev, struct phy_device *phy);
-
 #else
 static inline int phy_link_topo_add_phy(struct net_device *dev,
 					struct phy_device *phy,
@@ -72,6 +67,12 @@ static inline void phy_link_topo_del_phy(struct net_device *dev,
 					 struct phy_device *phy)
 {
 }
+
+static inline struct phy_device *
+phy_link_topo_get_phy(struct net_device *dev, u32 phyindex)
+{
+	return NULL;
+}
 #endif
 
 #endif /* __PHY_LINK_TOPOLOGY_H */
diff --git a/include/linux/phy_link_topology_core.h b/include/linux/phy_link_topology_core.h
index 0a6479055745..f9c0520806fb 100644
--- a/include/linux/phy_link_topology_core.h
+++ b/include/linux/phy_link_topology_core.h
@@ -2,24 +2,9 @@
 #ifndef __PHY_LINK_TOPOLOGY_CORE_H
 #define __PHY_LINK_TOPOLOGY_CORE_H
 
-struct phy_link_topology;
-
-#if IS_REACHABLE(CONFIG_PHYLIB)
-
-struct phy_link_topology *phy_link_topo_create(struct net_device *dev);
-void phy_link_topo_destroy(struct phy_link_topology *topo);
-
-#else
-
-static inline struct phy_link_topology *phy_link_topo_create(struct net_device *dev)
-{
-	return NULL;
-}
-
-static inline void phy_link_topo_destroy(struct phy_link_topology *topo)
-{
-}
-
-#endif
+struct phy_link_topology {
+	struct xarray phys;
+	u32 next_phy_index;
+};
 
 #endif /* __PHY_LINK_TOPOLOGY_CORE_H */
diff --git a/net/core/dev.c b/net/core/dev.c
index d2ce91a334c1..1b4ffc273a04 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -10256,6 +10256,35 @@ static void netdev_do_free_pcpu_stats(struct net_device *dev)
 	}
 }
 
+int netdev_alloc_phy_link_topology(struct net_device *dev)
+{
+	struct phy_link_topology *topo;
+
+	topo = kzalloc(sizeof(*topo), GFP_KERNEL);
+	if (!topo)
+		return -ENOMEM;
+
+	xa_init_flags(&topo->phys, XA_FLAGS_ALLOC1);
+	topo->next_phy_index = 1;
+
+	dev->link_topo = topo;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(netdev_alloc_phy_link_topology);
+
+static void netdev_free_phy_link_topology(struct net_device *dev)
+{
+	struct phy_link_topology *topo = dev->link_topo;
+
+	if (!topo)
+		return;
+
+	xa_destroy(&topo->phys);
+	kfree(topo);
+	dev->link_topo = NULL;
+}
+
 /**
  * register_netdevice() - register a network device
  * @dev: device to register
@@ -10998,11 +11027,6 @@ struct net_device *alloc_netdev_mqs(int sizeof_priv, const char *name,
 #ifdef CONFIG_NET_SCHED
 	hash_init(dev->qdisc_hash);
 #endif
-	dev->link_topo = phy_link_topo_create(dev);
-	if (IS_ERR(dev->link_topo)) {
-		dev->link_topo = NULL;
-		goto free_all;
-	}
 
 	dev->priv_flags = IFF_XMIT_DST_RELEASE | IFF_XMIT_DST_RELEASE_PERM;
 	setup(dev);
@@ -11092,7 +11116,9 @@ void free_netdev(struct net_device *dev)
 	free_percpu(dev->xdp_bulkq);
 	dev->xdp_bulkq = NULL;
 
-	phy_link_topo_destroy(dev->link_topo);
+#if IS_ENABLED(CONFIG_PHYLIB)
+	netdev_free_phy_link_topology(dev);
+#endif
 
 	/*  Compatibility with error handling in drivers */
 	if (dev->reg_state == NETREG_UNINITIALIZED ||
-- 
2.44.0