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 <buday.csaba@prolan.hu>
---
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(-)

diff --git a/drivers/net/mdio/fwnode_mdio.c b/drivers/net/mdio/fwnode_mdio.c
index ba7091518..8e8f9182a 100644
--- a/drivers/net/mdio/fwnode_mdio.c
+++ b/drivers/net/mdio/fwnode_mdio.c
@@ -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)
 {
@@ -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"))
+			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

On Fr, 2025-10-17 at 18:10 +0200, Buday Csaba wrote:
> 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 <buday.csaba@prolan.hu>
> ---
> 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.

>  - 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(-)
> 
> diff --git a/drivers/net/mdio/fwnode_mdio.c b/drivers/net/mdio/fwnode_mdio.c
> index ba7091518..8e8f9182a 100644
> --- a/drivers/net/mdio/fwnode_mdio.c
> +++ b/drivers/net/mdio/fwnode_mdio.c
> @@ -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)
>  {
> @@ -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

Thank you!
I do not know how that slipped.
I will fix it in v4.

Regards,
Csaba

On Mon, Oct 20, 2025 at 11:16:11AM +0200, Philipp Zabel wrote:
> On Fr, 2025-10-17 at 18:10 +0200, Buday Csaba wrote:
> > 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 <buday.csaba@prolan.hu>
> > ---
> > 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.
> 
> >  - 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(-)
> > 
> > diff --git a/drivers/net/mdio/fwnode_mdio.c b/drivers/net/mdio/fwnode_mdio.c
> > index ba7091518..8e8f9182a 100644
> > --- a/drivers/net/mdio/fwnode_mdio.c
> > +++ b/drivers/net/mdio/fwnode_mdio.c
> > @@ -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)
> >  {
> > @@ -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
>