Re: [PATCH net-next v2 3/3] net: mdio: treat PSE EPROBE_DEFER as non-fatal during PHY registration

[Andrew Lunn]

On Wed, Apr 08, 2026 at 11:07:11PM +0200, Carlo Szelinsky wrote:
> So I went ahead and tested the phy_probe() approach on my setup (RTL930x
> DSA switch with an I2C Hasivo HS104 PSE controller as module).
> 
> PoE itself works fine, but phydev->psec never gets set - ethtool just
> says "No PSE is attached" on all ports.
> 
> Took me a while to figure out what's going on. The problem is how DSA
> handles PHYs: when phy_probe() returns -EPROBE_DEFER because the PSE
> controller hasn't probed yet, the PHY device is registered but sits
> there unprobed. Then the DSA switch comes along, sets up its ports, and
> phy_attach_direct() force-binds the generic PHY driver with
> device_bind_driver(). Now the device already has a driver, so when the
> deferred probe retry kicks in it just skips it. phy_probe() never runs
> again and psec stays NULL.
> 
> What I'm seeing timing-wise:
>   - MDIO scan registers PHYs, phy_probe() defers (no PSE yet)
>   - DSA probes, phy_attach_direct() binds genphy
>   - t=17s: HS104 finally probes
>   - deferred retry: nope, driver already bound
>   - t=35s: regulator_late_cleanup (caught by admin_state_synced)
> 
> Not sure what the best path forward is here. Should we look at fixing
> phy_attach_direct() to handle this case, or go back to the non-fatal
> EPROBE_DEFER approach from v2 for now?

I thought about this some more. Looking at the phydev->drv might solve
it for DSA switches, but it is not a general solution for when the PSE
is used with a normal MAC, and the phylink_connect() happens in
open().

Now, the HS104 appears to be a quad device, intended for switches. So
maybe solving the issue only for DSA is O.K?

Otherwise, maybe we need the ability to associate the PSE controller
to the MAC? At a quick look, PSE and PHY are not tightly bound
together. So we could make the MAC driver call something similar to
of_pse_control_get() in its probe function, where it can return
EPRODE_DEFFER. net/ethtool/pse-pd.c would need some changes as well.

	Andrew