net: mdio: implement optional PHY reset before MDIO access

Some Ethernet PHYs require a hard reset before accessing their MDIO registers. When the ID is not provided by a compatible string, reading the PHY ID may fail on such devices.

This patch introduces a new device tree property called phy-id-read-needs-reset, which can be used to hard reset the PHY before attempting to read its ID via MDIO.

Signed-off-by Buday Csaba <[email protected]>

---
V2 -> V3: unchanged
V1 -> V2: added this DT binding

---
 Documentation/devicetree/bindings/net/ethernet-phy.yaml | 8 ++++++++
 1 file changed, 8 insertions(+)

Documentation/devicetree/bindings/net/ethernet-phy.yaml +8 -0

index 2ec2d9fda..b570f8038 100644
@@ -215,6 +215,14 @@ properties:
       Delay after the reset was deasserted in microseconds. If
       this property is missing the delay will be skipped.
 
+  phy-id-read-needs-reset:
+    $ref: /schemas/types.yaml#/definitions/flag
+    description:
+      Some PHYs require a hard reset before accessing MDIO registers.
+      This workaround allows auto-detection of the PHY ID in such cases.
+      When the PHY ID is provided with the 'compatible' string, setting
+      this property has no effect.
+
   sfp:
     $ref: /schemas/types.yaml#/definitions/phandle
     description:

Signature · 1 line

2.39.5

Implement support for the phy-id-read-needs-reset device tree property.

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 performs the hard-reset before attempting to read the ID, when the mentioned device tree property is present.

Signed-off-by Buday Csaba <[email protected]>

---
V2 -> V3: kernel-doc replaced with a comment (fixed warning) V1 -> V2:
- renamed DT property reset-phy-before-probe to phy-id-read-needs-reset

- 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 | 35 +++++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

drivers/net/mdio/fwnode_mdio.c +30 -0

index ba7091518..8e8f9182a 100644
@@ -114,6 +114,36 @@ 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;
+	}
+
+	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)
 {

Quoted 11 lines · Buday Csaba

Implement support for the phy-id-read-needs-reset device tree property.

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 performs the hard-reset before attempting to read the ID, when the mentioned device tree property is present.

Quoted 6 lines

Signed-off-by Buday Csaba <[email protected]>

---
V2 -> V3: kernel-doc replaced with a comment (fixed warning) V1 -> V2:
- renamed DT property reset-phy-before-probe to phy-id-read-needs-reset

Not completely, see below.

Quoted 50 lines

- 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 | 35 +++++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

drivers/net/mdio/fwnode_mdio.c +30 -0

index ba7091518..8e8f9182a 100644
@@ -114,6 +114,36 @@ 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;
+	}
+
+	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)
 {

drivers/net/mdio/fwnode_mdio.c int fwnode_mdiobus_register_phy(struct mii_bus *bus, · line 163

Quoted 6 lines

drivers/net/mdio/fwnode_mdio.c +2 -1

@@ -129,8 +159,11 @@ 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)) {
+		if (fwnode_property_present(child, "reset-phy-before-probe"))

Commit message says this should be "phy-id-read-needs-reset" now.

regards
Philipp