linux-kernel - Re: [PATCH net-next v3 4/4] net: mdio: reset PHY before attempting to access registers in fwnode_mdiobus_register

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Message-ID: <af5211fbb818c873f22b6622526fa8e0c9eb2fde.camel@pengutronix.de>
Date: Mon, 20 Oct 2025 11:16:11 +0200
From: Philipp Zabel <p.zabel@...gutronix.de>
To: Buday Csaba <buday.csaba@...lan.hu>, 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>, Rob Herring <robh@...nel.org>,  Krzysztof
 Kozlowski	 <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>,
 Florian Fainelli	 <f.fainelli@...il.com>, netdev@...r.kernel.org,
 devicetree@...r.kernel.org, 	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v3 4/4] net: mdio: reset PHY before attempting
 to access registers in fwnode_mdiobus_register_phy

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@...lan.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