[PATCH net] ixgbe: fix probing of multi-port devices with one MDIO

[Jakub Kicinski]

Ian reports that after upgrade from v5.8.14 to v5.9 only one
of his 4 ixgbe netdevs appear in the system.

Quoting the comment on ixgbe_x550em_a_has_mii():
 * Returns true if hw points to lowest numbered PCI B:D.F x550_em_a device in
 * the SoC.  There are up to 4 MACs sharing a single MDIO bus on the x550em_a,
 * but we only want to register one MDIO bus.

This matches the symptoms, since the return value from
ixgbe_mii_bus_init() is no longer ignored we need to handle
the higher ports of x550em without an error.

Fixes: 09ef193fef7e ("net: ethernet: ixgbe: check the return value of 
ixgbe_mii_bus_init()")
Reported-by: Ian Kumlien <ian.kuml...@gmail.com>
Signed-off-by: Jakub Kicinski <k...@kernel.org>
---
 drivers/net/ethernet/intel/ixgbe/ixgbe_phy.c | 23 ++++++++++++--------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_phy.c 
b/drivers/net/ethernet/intel/ixgbe/ixgbe_phy.c
index f77fa3e4fdd1..fc389eecdd2b 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_phy.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_phy.c
@@ -901,15 +901,13 @@ static bool ixgbe_x550em_a_has_mii(struct ixgbe_hw *hw)
  **/
 s32 ixgbe_mii_bus_init(struct ixgbe_hw *hw)
 {
+       s32 (*write)(struct mii_bus *bus, int addr, int regnum, u16 val);
+       s32 (*read)(struct mii_bus *bus, int addr, int regnum);
        struct ixgbe_adapter *adapter = hw->back;
        struct pci_dev *pdev = adapter->pdev;
        struct device *dev = &adapter->netdev->dev;
        struct mii_bus *bus;
 
-       bus = devm_mdiobus_alloc(dev);
-       if (!bus)
-               return -ENOMEM;
-
        switch (hw->device_id) {
        /* C3000 SoCs */
        case IXGBE_DEV_ID_X550EM_A_KR:
@@ -922,16 +920,23 @@ s32 ixgbe_mii_bus_init(struct ixgbe_hw *hw)
        case IXGBE_DEV_ID_X550EM_A_1G_T:
        case IXGBE_DEV_ID_X550EM_A_1G_T_L:
                if (!ixgbe_x550em_a_has_mii(hw))
-                       return -ENODEV;
-               bus->read = &ixgbe_x550em_a_mii_bus_read;
-               bus->write = &ixgbe_x550em_a_mii_bus_write;
+                       return 0;
+               read = &ixgbe_x550em_a_mii_bus_read;
+               write = &ixgbe_x550em_a_mii_bus_write;
                break;
        default:
-               bus->read = &ixgbe_mii_bus_read;
-               bus->write = &ixgbe_mii_bus_write;
+               read = &ixgbe_mii_bus_read;
+               write = &ixgbe_mii_bus_write;
                break;
        }
 
+       bus = devm_mdiobus_alloc(dev);
+       if (!bus)
+               return -ENOMEM;
+
+       bus->read = read;
+       bus->write = write;
+
        /* Use the position of the device in the PCI hierarchy as the id */
        snprintf(bus->id, MII_BUS_ID_SIZE, "%s-mdio-%s", ixgbe_driver_name,
                 pci_name(pdev));
-- 
2.26.2