Re: [PATCH net] net: phy: add device link between MAC device and MDIO device

[Maxime Chevallier <maxime.chevallier@bootlin.com>]

Hi

[...]
> 
> diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
> index 81984d4ebb7c..d5ac7506fe39 100644
> --- a/drivers/net/phy/phy_device.c
> +++ b/drivers/net/phy/phy_device.c
> @@ -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 ?

> -	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.

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.

Maxime