netdev - Re: [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: <aQIhf3dXOxS4vd2W@debianbuilder>
Date: Wed, 29 Oct 2025 15:15:27 +0100
From: Buday Csaba <buday.csaba@...lan.hu>
To: Andrew Lunn <andrew@...n.ch>
CC: 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>
Subject: Re: [PATCH net-next v5 3/4] net: mdio: reset PHY before attempting
 to access registers in fwnode_mdiobus_register_phy

On Wed, Oct 29, 2025 at 02:20:14PM +0100, Andrew Lunn wrote:
> > +/* 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);
> 
> You add a _get() here. Where is the corresponding _put()?

When mdio_device_free() is called, it eventually invokes
mdio_device_release(). There is the corresponding _put(), that will
release the reference. I also verified this with a stack trace.

> 
> Also, fwnode_handle_get() returns a handle. Why do you throw it away?
> What is the point of this get?
>

I copied this initialization stub from of_mdiobus_register_device()
in of_mdio.c. The same pattern is used there:

	fwnode_handle_get(fwnode);
	device_set_node(&mdiodev->dev, fwnode);

It is kind of awkward that we need to half-establish a device, just
to assert the reset, but I could not think of any better solution, that
does not lead to a large amount of code duplication.

> > +	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;
> > +}
> > +
> 
> 	Andrew
> 

Csaba