linux-kernel - RE: [PATCH net] net: phy: add device link between MAC device and MDIO device

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Message-ID:
 <PAXPR04MB85100B7C2C6738CEA80C3C7D889EA@PAXPR04MB8510.eurprd04.prod.outlook.com>
Date: Thu, 29 Jan 2026 10:00:37 +0000
From: Wei Fang <wei.fang@....com>
To: Maxime Chevallier <maxime.chevallier@...tlin.com>
CC: "imx@...ts.linux.dev" <imx@...ts.linux.dev>, "netdev@...r.kernel.org"
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Subject: RE: [PATCH net] net: phy: add device link between MAC device and MDIO
 device

> > @@ -1768,12 +1768,21 @@ int phy_attach_direct(struct net_device *dev,
> struct phy_device *phydev,
> >
> >  	/**
> >  	 * If the external phy used by current mac interface is managed by
> > -	 * another mac interface, so we should create a device link between
> > -	 * phy dev and mac dev.
> > +	 * another MDIO controller, which means that the MAC and MDIO are
> > +	 * separated devices, then we should create a device link between
> > +	 * the MAC device and the MDIO device.
> >  	 */
> 
> I was confused by the use of the "MDIO device" terminology here, which
> refers to a device sitting on an mdio bus, such as a PHY. I think though
> that what you actually refer to is the MDIO controller itself, right ?

Yes, you are right, I was referring to the MDIO controller.

> 
> > -	if (dev && phydev->mdio.bus->parent && dev->dev.parent !=
> phydev->mdio.bus->parent)
> > -		phydev->devlink = device_link_add(dev->dev.parent,
> &phydev->mdio.dev,
> > -						  DL_FLAG_PM_RUNTIME |
> DL_FLAG_STATELESS);
> > +	if (dev && phydev->mdio.bus->parent &&
> > +	    dev->dev.parent != phydev->mdio.bus->parent) {
> > +		if (!device_link_add(dev->dev.parent, phydev->mdio.bus->parent,
> > +				     DL_FLAG_PM_RUNTIME |
> > +				     DL_FLAG_AUTOREMOVE_SUPPLIER)) {
> 
> Don't we have the same problem with SFP ? The struct mii_bus for SFP
> PHYs also completely disappears when you remove the module.

Sorry, I'm not familiar with SFP and I do not have a board with SPF
module. So I'm not sure whether the MDIO bus will be removed if
the SFP module is unplugged. But if the multiple SPF modules share
the same MDIO controller, unplugging one SFP module will cause the
MDIO bus to be removed. Won't this cause the other SFP modules to
stop working?

> 
> That being said, I ran some tests with SFP and this patch, and the
> netdev actually didn't dissapear under my feet.
> 
> I'm a total noob with fw_devlink, but I can see there seems to already
> be a link between MAC devices and the associated SFP bus :
> 
> on cyclone V :
> 
> # ls /sys/class/devlink
>  [...]
> platform:sfp--platform:ff702000.ethernet
> 
> on macchiatobin :
> 
> # ls /sys/class/devlink
>  [...]
> platform:sfp-eth3--platform:f4000000.ethernet
> 
> So I guess this is what's preventing the netdev from going away.
> 
> Now, these seems to be automagically populated based on DT, but I don't
> know if it also works with non-DT platforms. If this is DT-specific,
> then I guess we still can't use DL_FLAG_AUTOREMOVE_SUPPLIER.
> 

Previously, when Sorash attempted to add
DL_FLAG_AUTOREMOVE_SUPPLIER to the devlink between the MAC
controller and the PHY, you reported that unplugging the PHY would
cause the MAC to be removed as well, resulting in system hangs.

https://lore.kernel.org/imx/20250704142138.3f1a4ec1@fedora.home/

If your guess is correct, removing the SPF module will cause the
MDIO bus to be removed, then I think the MAC driver should also
be removed. Therefore, based on this patch, you should be able
to reproduce the same problem caused by the Sorash's patch.
However, your current results seem different from before. Perhaps
the MDIO bus was not removed along with the SFP module.