linux-kernel - Re: [RFC net-next 0/2] Introduce MDIO probe order C45 over C22

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Date:   Sat, 5 Jun 2021 08:37:22 +0800
From:   Wong Vee Khee <vee.khee.wong@...ux.intel.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC net-next 0/2] Introduce MDIO probe order C45 over C22

Hi Andrew,

On Thu, Jun 03, 2021 at 07:51:55AM +0800, Wong Vee Khee wrote:
> On Wed, Jun 02, 2021 at 05:03:52PM +0200, Andrew Lunn wrote:
> > > I took a look at how most ethernet drivers implement their "bus->read"
> > > function. Most of them either return -EIO or -ENODEV.
> > > 
> > > I think it safe to drop the return error type when we try with C45 access:
> > > 
> > > 
> > > diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
> > > index 1539ea021ac0..282d16fdf6e1 100644
> > > --- a/drivers/net/phy/phy_device.c
> > > +++ b/drivers/net/phy/phy_device.c
> > > @@ -870,6 +870,18 @@ struct phy_device *get_phy_device(struct mii_bus *bus, int addr, bool is_c45)
> > >         if (r)
> > >                 return ERR_PTR(r);
> > > 
> > > +       /* PHY device such as the Marvell Alaska 88E2110 will return a PHY ID
> > > +        * of 0 when probed using get_phy_c22_id() with no error. Proceed to
> > > +        * probe with C45 to see if we're able to get a valid PHY ID in the C45
> > > +        * space, if successful, create the C45 PHY device.
> > > +        */
> > > +       if ((!is_c45) && (phy_id == 0)) {
> > > +               r = get_phy_c45_ids(bus, addr, &c45_ids);
> > > +               if (!r)
> > > +                       return phy_device_create(bus, addr, phy_id,
> > > +                                                true, &c45_ids);
> > > +       }
> > 
> > This is getting better. But look at for example
> > drivers/net/mdio/mdio-bcm-unimac.c. What will happen when you ask it
> > to do get_phy_c45_ids()?
> >
> 
> I will add an additional check for bus->probe_capabilities. This will ensure
> that only a MDIO bus that is capable for C45 access will go for the 'try getting
> PHY ID from C45 space' approach. Currently, only Freescale's QorIQ 10G MDIO
> Controller driver and STMMAC driver has a bus->probe_capabilities of > MDIOBUS_C45.
> So, I would say with this additional checking, it would not break most of the drivers:-
> 
> 
> diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
> index 1539ea021ac0..460c0866ac84 100644
> --- a/drivers/net/phy/phy_device.c
> +++ b/drivers/net/phy/phy_device.c
> @@ -870,6 +870,19 @@ struct phy_device *get_phy_device(struct mii_bus *bus, int addr, bool is_c45)
>         if (r)
>                 return ERR_PTR(r);
> 
> +       /* PHY device such as the Marvell Alaska 88E2110 will return a PHY ID
> +        * of 0 when probed using get_phy_c22_id() with no error. Proceed to
> +        * probe with C45 to see if we're able to get a valid PHY ID in the C45
> +        * space, if successful, create the C45 PHY device.
> +        */
> +       if ((!is_c45) && (phy_id == 0) &&
> +            (bus->probe_capabilities >= MDIOBUS_C45)) {
> +               r = get_phy_c45_ids(bus, addr, &c45_ids);
> +               if (!r)
> +                       return phy_device_create(bus, addr, phy_id,
> +                                                true, &c45_ids);
> +       }
> +
>         return phy_device_create(bus, addr, phy_id, is_c45, &c45_ids);
>  }
>  EXPORT_SYMBOL(get_phy_device);
> 

Can you take a look at the latest implementation and provide
feedback?

VK