netdev - [PATCH net-next v5 3/4] net: mdio: reset PHY before attempting to access registers in fwnode_mdiobus_register

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Message-ID: <5f8d93021a7aa6eeb4fb67ab27ddc7de9101c59f.1761732347.git.buday.csaba@prolan.hu>
Date: Wed, 29 Oct 2025 11:23:43 +0100
From: Buday Csaba <buday.csaba@...lan.hu>
To: Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>, "David S. Miller"
	<davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
	<kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Philipp Zabel
	<p.zabel@...gutronix.de>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
CC: Buday Csaba <buday.csaba@...lan.hu>
Subject: [PATCH net-next v5 3/4] net: mdio: reset PHY before attempting to access registers in fwnode_mdiobus_register_phy

When the ID of an Ethernet PHY is not provided by the 'compatible'
string in the device tree, its actual ID is read via the MDIO bus.
For some PHYs this could be unsafe, since a hard reset may be
necessary to safely access the MDIO registers.

Add a fallback mechanism for these devices: when reading the
ID fails, the reset will be asserted, and the ID read is retried.

Signed-off-by: Buday Csaba <buday.csaba@...lan.hu>
---
V4 -> V5:
 - when fwnode_reset_phy() returns with -EPROBE_DEFER, that error
   is now propagated upstream instead of being discarded.
 - info message removed (it will be a separate commit)
 - 'err' variable changed to 'rc' in fwnode_reset_phy()
 - removed last fwnode_handle_put() in fwnode_reset_phy()
   The cleanup is performed by mdio_device_free().
V3 -> V4: dropped DT property `phy-id-read-needs-reset` to control
	  the reset behaviour, asserting reset as a fallback
	  mechanism instead. Added info level message for resetting.
V2 -> V3: kernel-doc replaced with a comment (fixed warning)
V1 -> V2:
 - renamed fwnode_reset_phy_before_probe() to
   fwnode_reset_phy()
 - added kernel-doc for fwnode_reset_phy()
 - improved error handling in fwnode_reset_phy()
---
 drivers/net/mdio/fwnode_mdio.c | 38 +++++++++++++++++++++++++++++++++-
 1 file changed, 37 insertions(+), 1 deletion(-)

diff --git a/drivers/net/mdio/fwnode_mdio.c b/drivers/net/mdio/fwnode_mdio.c
index ba7091518..9669da2b7 100644
--- a/drivers/net/mdio/fwnode_mdio.c
+++ b/drivers/net/mdio/fwnode_mdio.c
@@ -114,6 +114,34 @@ int fwnode_mdiobus_phy_device_register(struct mii_bus *mdio,
 }
 EXPORT_SYMBOL(fwnode_mdiobus_phy_device_register);
 
+/* Hard-reset a PHY before registration */
+static int fwnode_reset_phy(struct mii_bus *bus, u32 addr,
+			    struct fwnode_handle *phy_node)
+{
+	struct mdio_device *tmpdev;
+	int rc;
+
+	tmpdev = mdio_device_create(bus, addr);
+	if (IS_ERR(tmpdev))
+		return PTR_ERR(tmpdev);
+
+	fwnode_handle_get(phy_node);
+	device_set_node(&tmpdev->dev, phy_node);
+	rc = mdio_device_register_reset(tmpdev);
+	if (rc) {
+		mdio_device_free(tmpdev);
+		return rc;
+	}
+
+	mdio_device_reset(tmpdev, 1);
+	mdio_device_reset(tmpdev, 0);
+
+	mdio_device_unregister_reset(tmpdev);
+	mdio_device_free(tmpdev);
+
+	return 0;
+}
+
 int fwnode_mdiobus_register_phy(struct mii_bus *bus,
 				struct fwnode_handle *child, u32 addr)
 {
@@ -129,8 +157,16 @@ int fwnode_mdiobus_register_phy(struct mii_bus *bus,
 		return PTR_ERR(mii_ts);
 
 	is_c45 = fwnode_device_is_compatible(child, "ethernet-phy-ieee802.3-c45");
-	if (is_c45 || fwnode_get_phy_id(child, &phy_id))
+	if (is_c45 || fwnode_get_phy_id(child, &phy_id)) {
 		phy = get_phy_device(bus, addr, is_c45);
+		if (IS_ERR(phy)) {
+			rc = fwnode_reset_phy(bus, addr, child);
+			if (rc == -EPROBE_DEFER)
+				goto clean_mii_ts;
+			else if (!rc)
+				phy = get_phy_device(bus, addr, is_c45);
+		}
+	}
 	else
 		phy = phy_device_create(bus, addr, phy_id, 0, NULL);
 	if (IS_ERR(phy)) {
-- 
2.39.5