[PATCH net-next v2 2/5] of: mdio: Scan PHY address 0 last
From: Jakub Vaněk <hidden>
Date: 2026-02-28 23:23:06
Also in:
lkml
Subsystem:
ethernet phy library, networking drivers, the rest · Maintainers:
Andrew Lunn, Heiner Kallweit, Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
Some PHY devices incorrectly treat address 0 as a broadcast address.
As a result, accesses to address 0 may cause multiple PHYs to respond,
making one or both PHYs work unreliably.
On several PHYs (e.g. Motorcomm YT8821 and Realtek RTL8221B), this
behavior can be disabled via a vendor-specific internal register.
However, for that to be useful, that register would have to be
programmed before address 0 is accessed for the first time.
Device Tree-based systems scan MDIO buses via of_mdiobus_register().
Modify the scanning order so that address 0 is scanned last. This
ensures PHY fixups for addresses 1-31 are applied before address 0
is accessed, allowing the collision to be prevented.
However, preserve the original probing order for one edge case: when
the Device Tree does not explicitly specify PHY addresses. In that
scenario, PHY DT nodes appear to be matched to devices based on a
sequential bus scan. Changing the scanning sequence could change
the association between DT nodes and PHY devices and potentially break
existing setups.
For example, with:
mdio-bus {
phy0: ethernet-phy {
compatible = "ethernet-phy-id1234.5678";
};
phy1: ethernet-phy {
compatible = "ethernet-phy-id90AB.CDEF";
};
};
scanning address 0 last could cause the PHY on address 0 to be associated
with the phy1 node.
Suggested-by: Daniel Golle <daniel@makrotopia.org>
Signed-off-by: Jakub Vaněk <redacted>
---
drivers/net/mdio/of_mdio.c | 35 +++++++++++++++++++++++++++++++----
1 file changed, 31 insertions(+), 4 deletions(-)
diff --git a/drivers/net/mdio/of_mdio.c b/drivers/net/mdio/of_mdio.c
index b8d298c04d3f..a705991f6b04 100644
--- a/drivers/net/mdio/of_mdio.c
+++ b/drivers/net/mdio/of_mdio.c@@ -27,6 +27,11 @@ MODULE_AUTHOR("Grant Likely <grant.likely@secretlab.ca>"); MODULE_LICENSE("GPL"); MODULE_DESCRIPTION("OpenFirmware MDIO bus (Ethernet PHY) accessors"); +enum scan_phase { + SCAN_PHASE_NOT_PHYAD_0, + SCAN_PHASE_PHYAD_0, +}; + /* Extract the clause 22 phy ID from the compatible string of the form * ethernet-phy-idAAAA.BBBB */ static int of_get_phy_id(struct device_node *device, u32 *phy_id)
@@ -137,7 +142,7 @@ bool of_mdiobus_child_is_phy(struct device_node *child) EXPORT_SYMBOL(of_mdiobus_child_is_phy); static int __of_mdiobus_parse_phys(struct mii_bus *mdio, struct device_node *np, - bool *scanphys) + bool *scanphys, enum scan_phase phase) { struct device_node *child; int addr, rc = 0;
@@ -149,7 +154,7 @@ static int __of_mdiobus_parse_phys(struct mii_bus *mdio, struct device_node *np, if (!of_property_present(child, "reg")) continue; - rc = __of_mdiobus_parse_phys(mdio, child, NULL); + rc = __of_mdiobus_parse_phys(mdio, child, NULL, phase); if (rc && rc != -ENODEV) goto exit;
@@ -164,6 +169,12 @@ static int __of_mdiobus_parse_phys(struct mii_bus *mdio, struct device_node *np, continue; } + if (phase == SCAN_PHASE_NOT_PHYAD_0 && addr == 0) + continue; + + if (phase == SCAN_PHASE_PHYAD_0 && addr != 0) + continue; + if (of_mdiobus_child_is_phy(child)) rc = of_mdiobus_register_phy(mdio, child, addr); else
@@ -223,8 +234,19 @@ int __of_mdiobus_register(struct mii_bus *mdio, struct device_node *np, if (rc) return rc; - /* Loop over the child nodes and register a phy_device for each phy */ - rc = __of_mdiobus_parse_phys(mdio, np, &scanphys); + /* Loop over the child nodes and register a phy_device for each phy. + * However, scan address 0 last. Some vendors consider it a broadcast + * address and so their PHYs respond at it in addition to the actual PHY + * address. Scanning addresses 1-31 first allows PHY fixups to stop + * the potential collision at address 0 from occurring. + */ + rc = __of_mdiobus_parse_phys(mdio, np, &scanphys, + SCAN_PHASE_NOT_PHYAD_0); + if (rc) + goto unregister; + + rc = __of_mdiobus_parse_phys(mdio, np, &scanphys, + SCAN_PHASE_PHYAD_0); if (rc) goto unregister;
@@ -238,6 +260,11 @@ int __of_mdiobus_register(struct mii_bus *mdio, struct device_node *np, of_node_name_eq(child, "ethernet-phy-package")) continue; + /* Skip the SCAN_PHASE_NOT_PHYAD_0/SCAN_PHASE_PHYAD_0 + * stuff here. Some device tree setups may assume linear + * assignment from address 0 onwards and the two-pass probing + * is not worth breaking these setups. + */ for (addr = 0; addr < PHY_MAX_ADDR; addr++) { /* skip already registered PHYs */ if (mdiobus_is_registered_device(mdio, addr))
--
2.43.0