Subject: Re: [RFC net-next 1/2] net: phy: allow mdio bus to probe for c45 devices before c22

From: Wong Vee Khee <[email-masked]>
Date: Tue, 1 Jun 2021 18:52:31 +0800

On Tue, May 25, 2021 at 09:31:17AM +0100, Russell King (Oracle) wrote:
> On Tue, May 25, 2021 at 01:58:39PM +0800, Wong Vee Khee wrote:
> > Some MAC controllers that is able to pair with  external PHY devices
> > such as the Synopsys MAC Controller (STMMAC) support both Clause-22 and
> > Clause-45 access.
> > 
> > When paired with PHY devices that only accessible via Clause-45, such as
> > the Marvell 88E2110, any attempts to access the PHY devices via
> > Clause-22 will get a PHY ID of all zeroes.
> > 
> > To fix this, we introduce MDIOBUS_C45_C22 which the MAC controller will
> > try with Clause-45 access before going to Clause-22.
> > 
> > Signed-off-by: Wong Vee Khee <[email-masked]>
> > ---
> >  include/linux/phy.h | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/include/linux/phy.h b/include/linux/phy.h
> > index 60d2b26026a2..9b0e2c76e19b 100644
> > --- a/include/linux/phy.h
> > +++ b/include/linux/phy.h
> > @@ -368,6 +368,7 @@ struct mii_bus {
> >  		MDIOBUS_C22,
> >  		MDIOBUS_C45,
> >  		MDIOBUS_C22_C45,
> > +		MDIOBUS_C45_C22,
> >  	} probe_capabilities;
> >  
> >  	/** @shared_lock: protect access to the shared element */
> 
> The new definition doesn't seem to be used anywhere, so this patch
> merely adds the definition. It doesn't do what it says in the subject
> line. Any driver that sets the capabilities to MDIOBUS_C45_C22 will
> end up not doing any probing of the PHY.
>

You are right. I left out the required changes in drivers/net/mdio_bus.c:-

diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c
index 6045ad3def12..fbf9b8f1f47c 100644
--- a/drivers/net/phy/mdio_bus.c
+++ b/drivers/net/phy/mdio_bus.c
@@ -684,6 +684,11 @@ struct phy_device *mdiobus_scan(struct mii_bus *bus, int addr)
                if (IS_ERR(phydev))
                        phydev = get_phy_device(bus, addr, true);
                break;
+       case MDIOBUS_C45_C22:
+               phydev = get_phy_device(bus, addr, true);
+               if (IS_ERR(phydev))
+                       phydev = get_phy_device(bus, addr, false);
+               break;
        }

        if (IS_ERR(phydev))

VK