net: stmmac: the XPCS obscures a potential "PHY not found" error

stmmac_mdio_register() has logic to search for PHYs on the MDIO bus and
assign them IRQ lines, as well as to set priv->plat->phy_addr.

If no PHY is found, the "found" variable remains set to 0 and the
function errors out.

After the introduction of commit f213bbe8a9d6 ("net: stmmac: Integrate
it with DesignWare XPCS"), the "found" variable was immediately reused
for searching for a PCS on the same MDIO bus.

This can result in 2 types of potential problems (none of them seems to
be seen on the only Intel system that sets has_xpcs = true, otherwise it
would have been reported):

1. If a PCS is found but a PHY is not, then the code happily exits with
   no error. One might say "yes, but this is not possible, because
   of_mdiobus_register will probe a PHY for all MDIO addresses,
   including for the XPCS, so if an XPCS exists, then a PHY certainly
   exists too". Well, that is not true, see intel_mgbe_common_data():

	/* Ensure mdio bus scan skips intel serdes and pcs-xpcs */
	plat->mdio_bus_data->phy_mask = 1 << INTEL_MGBE_ADHOC_ADDR;
	plat->mdio_bus_data->phy_mask |= 1 << INTEL_MGBE_XPCS_ADDR;

2. A PHY is found but an MDIO device with the XPCS PHY ID isn't, and in
   that case, the error message will be "No PHY found". Confusing.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20210527155959.3270478-1-olteanv@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c
index b750074..e293bf1 100644 (file)
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_mdio.c
@@ -503,6 +503,12 @@ int stmmac_mdio_register(struct net_device *ndev)
                found = 1;
        }
 
+       if (!found && !mdio_node) {
+               dev_warn(dev, "No PHY found\n");
+               err = -ENODEV;
+               goto no_phy_found;
+       }
+
        /* Try to probe the XPCS by scanning all addresses. */
        if (priv->hw->xpcs) {
                struct mdio_xpcs_args *xpcs = &priv->hw->xpcs_args;
@@ -511,6 +517,7 @@ int stmmac_mdio_register(struct net_device *ndev)
 
                xpcs->bus = new_bus;
 
+               found = 0;
                for (addr = 0; addr < max_addr; addr++) {
                        xpcs->addr = addr;
 
@@ -520,13 +527,12 @@ int stmmac_mdio_register(struct net_device *ndev)
                                break;
                        }
                }
-       }
 
-       if (!found && !mdio_node) {
-               dev_warn(dev, "No PHY found\n");
-               mdiobus_unregister(new_bus);
-               mdiobus_free(new_bus);
-               return -ENODEV;
+               if (!found && !mdio_node) {
+                       dev_warn(dev, "No XPCS found\n");
+                       err = -ENODEV;
+                       goto no_xpcs_found;
+               }
        }
 
 bus_register_done:
@@ -534,6 +540,9 @@ bus_register_done:
 
        return 0;
 
+no_xpcs_found:
+no_phy_found:
+       mdiobus_unregister(new_bus);
 bus_register_fail:
        mdiobus_free(new_bus);
        return err;