Re: [net-next,v2,09/15] net: ftgmac100: Always register the MDIO bus when it exists

On Tue, Jan 20, 2026 at 12:14:07PM +0000, Simon Horman wrote:

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---
net: ftgmac100: Always register the MDIO bus when it exists

This patch moves MDIO bus registration earlier in the probe function
for FARADAY, AST2400, and AST2500 MACs, simplifying the code by
registering it unconditionally when the hardware has an MDIO controller.

Note: These issues appear to be fixed later in the series by commits
8961daa5f2c0 ("Simplify error handling for ftgmac100_setup_mdio") and
046e51399f0f ("Move DT probe into a helper").

quoted

diff --git a/drivers/net/ethernet/faraday/ftgmac100.c b/drivers/net/ethernet/faraday/ftgmac100.c
index f1cb5dc37919..931fdf3d07d1 100644
--- a/drivers/net/ethernet/faraday/ftgmac100.c
+++ b/drivers/net/ethernet/faraday/ftgmac100.c

@@ -1957,6 +1957,14 @@ static int ftgmac100_probe(struct platform_device *pdev)
 		priv->txdes0_edotr_mask = BIT(15);
 	}

+	if (priv->mac_id == FTGMAC100_FARADAY ||
+	    priv->mac_id == FTGMAC100_AST2400 ||
+	    priv->mac_id == FTGMAC100_AST2500) {
+		err = ftgmac100_setup_mdio(netdev);
+		if (err)
+			goto err_phy_connect;
+	}

If ftgmac100_setup_mdio() fails after of_mdiobus_register() returns an
error, it calls mdiobus_free(priv->mii_bus) but does not set priv->mii_bus
to NULL. The goto err_phy_connect then leads to ftgmac100_destroy_mdio()
which checks if (!priv->mii_bus) but finds a dangling pointer, resulting
in mdiobus_unregister() on freed memory followed by a double free.

The call to register the MDIO bus has been moved earlier. That means
the call to ftgmac100_destroy_mdio() the bus also needs to move
earlier on the error cleanup path, before err_phy_connect:

	Andrew