[PATCH iwl-net v2] ixgbe: fix MDIO bus lifetime

[Richard Patel <ripatel@wii.dev>]

Plugging in an unsupported SFP module caused ixgbe NICs to get
wedged permanently.

ixgbe unregisters the netdev when rejecting an SFP transceiver as
unsupported.

  ixgbe 0000:3b:00.0: failed to initialize because an unsupported SFP+ module type was detected.
  ixgbe 0000:3b:00.0: Reload the driver after installing a supported module.
  ixgbe 0000:3b:00.0: removed PHC on enp59s0

This code path failed to unregister an MDIO bus owned by that
netdev, so when unregister_netdev() tries to tear it down
(via device_del() -> devres_release_all() -> mdiobus_free()),
it trips over the leaked registration.

  ixgbe-mdio-0000:3b:00.0: not in UNREGISTERED state
  WARNING: drivers/net/phy/mdio_bus_provider.c:711 at mdiobus_free+0x3d/0x50, CPU#21: kworker/u128:0/12

This prevents ixgbe from reloading, even after PCIe remove/rescan:

  sysfs: cannot create duplicate filename '/class/mdio_bus/ixgbe-mdio-0000:3b:00.0'

Switch to devm_mdiobus_register(), drop custom unregister calls.
This is safe because the bus is already devm-allocated, so unregister
always happens before free.

Assisted-by: LLM
Fixes: 8fa10ef01260 ("ixgbe: register a mdiobus")
Suggested-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Richard Patel <ripatel@wii.dev>
---
v1 -> v2: use devm_mdiobus_register() instead of another
          mdiobus_unregister() call
v1: https://lore.kernel.org/netdev/20260826042945.2344686-1-ripatel@wii.dev/

 drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 9 ++-------
 drivers/net/ethernet/intel/ixgbe/ixgbe_phy.c  | 2 +-
 2 files changed, 3 insertions(+), 8 deletions(-)

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
index f91856498eb2..96f60269fca6 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -8471,6 +8471,7 @@ static void ixgbe_sfp_detection_subtask(struct ixgbe_adapter *adapter)
 		e_dev_err("Reload the driver after installing a "
 			  "supported module.\n");
 		unregister_netdev(adapter->netdev);
+		adapter->mii_bus = NULL;
 	}
 }
 
@@ -8693,11 +8694,8 @@ static void ixgbe_service_task(struct work_struct *work)
 	}
 	if (ixgbe_check_fw_error(adapter)) {
 		if (!test_bit(__IXGBE_DOWN, &adapter->state)) {
-			if (adapter->mii_bus) {
-				mdiobus_unregister(adapter->mii_bus);
-				adapter->mii_bus = NULL;
-			}
 			unregister_netdev(adapter->netdev);
+			adapter->mii_bus = NULL;
 		}
 		ixgbe_service_event_complete(adapter);
 		return;
@@ -12104,9 +12102,6 @@ static void ixgbe_remove(struct pci_dev *pdev)
 	if (adapter->hw.mac.type == ixgbe_mac_e610)
 		ixgbe_disable_link_status_events(adapter);
 
-	if (adapter->mii_bus)
-		mdiobus_unregister(adapter->mii_bus);
-
 #ifdef CONFIG_IXGBE_DCA
 	if (adapter->flags & IXGBE_FLAG_DCA_ENABLED) {
 		adapter->flags &= ~IXGBE_FLAG_DCA_ENABLED;
diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_phy.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_phy.c
index ab733e73927d..74631cb2ddbc 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_phy.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_phy.c
@@ -1086,7 +1086,7 @@ int ixgbe_mii_bus_init(struct ixgbe_hw *hw)
 	hw->phy.mdio.mode_support = MDIO_SUPPORTS_C45 | MDIO_SUPPORTS_C22;
 
 	adapter->mii_bus = bus;
-	return mdiobus_register(bus);
+	return devm_mdiobus_register(dev, bus);
 }
 
 /**
-- 
2.52.0