[PATCH 4.19 14/36] net: stmmac: Handle disabled MDIO busses from devicetree

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andrew Halaney <ahalaney@redhat.com>

[ Upstream commit e23c0d21ce9234fbc31ece35663ababbb83f9347 ]

Many hardware configurations have the MDIO bus disabled, and are instead
using some other MDIO bus to talk to the MAC's phy.

of_mdiobus_register() returns -ENODEV in this case. Let's handle it
gracefully instead of failing to probe the MAC.

Fixes: 47dd7a540b8a ("net: add support for STMicroelectronics Ethernet controllers.")
Signed-off-by: Andrew Halaney <ahalaney@redhat.com>
Reviewed-by: Serge Semin <fancer.lancer@gmail.com>
Link: https://lore.kernel.org/r/20231212-b4-stmmac-handle-mdio-enodev-v2-1-600171acf79f@redhat.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c
@@ -360,7 +360,11 @@ int stmmac_mdio_register(struct net_devi
 	new_bus->parent = priv->device;
 
 	err = of_mdiobus_register(new_bus, mdio_node);
-	if (err != 0) {
+	if (err == -ENODEV) {
+		err = 0;
+		dev_info(dev, "MDIO bus is disabled\n");
+		goto bus_register_fail;
+	} else if (err) {
 		dev_err(dev, "Cannot register the MDIO bus\n");
 		goto bus_register_fail;
 	}