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 f213bbe8a9 ("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>
4751d2aa32