netdev - [PATCH net-next v4 4/4] net: mdio: reset PHY before attempting to access registers in fwnode_mdiobus_register

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Message-ID: <bebbaef2c6801f6973ea00500a594ed934e40e47.1761124022.git.buday.csaba@prolan.hu>
Date: Wed, 22 Oct 2025 11:08:53 +0200
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 v4 4/4] 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.

This patch adds a fallback mechanism for these devices:
when reading the ID fails, the reset will be asserted, and the
ID read is retried.
When the reset is asserted, an info level message is printed.

Signed-off-by: Buday Csaba <buday.csaba@...lan.hu>
---
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 | 41 +++++++++++++++++++++++++++++++++-
 1 file changed, 40 insertions(+), 1 deletion(-)

diff --git a/drivers/net/mdio/fwnode_mdio.c b/drivers/net/mdio/fwnode_mdio.c
index ba7091518..623120e3b 100644
--- a/drivers/net/mdio/fwnode_mdio.c
+++ b/drivers/net/mdio/fwnode_mdio.c
@@ -114,6 +114,40 @@ 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 err;
+
+	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);
+	err = mdio_device_register_reset(tmpdev);
+	if (err) {
+		mdio_device_free(tmpdev);
+		return err;
+	}
+
+	if (mdio_device_has_reset(tmpdev)) {
+		dev_info(&bus->dev,
+			 "PHY device at address %d not detected, resetting PHY.",
+			 addr);
+		mdio_device_reset(tmpdev, 1);
+		mdio_device_reset(tmpdev, 0);
+	}
+
+	mdio_device_unregister_reset(tmpdev);
+	mdio_device_free(tmpdev);
+	fwnode_handle_put(phy_node);
+
+	return 0;
+}
+
 int fwnode_mdiobus_register_phy(struct mii_bus *bus,
 				struct fwnode_handle *child, u32 addr)
 {
@@ -129,8 +163,13 @@ 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)) {
+			fwnode_reset_phy(bus, addr, child);
+			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