netdev - Re: [PATCH net-next v4 05/11] net: dsa: realtek: use phy

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Date:   Fri, 21 Jan 2022 19:13:07 -0300
From:   Luiz Angelo Daros de Luca <luizluca@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        "open list:NETWORKING DRIVERS" <netdev@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Alvin Šipraga <alsi@...g-olufsen.dk>,
        Arınç ÜNAL <arinc.unal@...nc9.com>,
        Frank Wunderlich <frank-w@...lic-files.de>
Subject: Re: [PATCH net-next v4 05/11] net: dsa: realtek: use phy_read in ds->ops

---
> > Thanks, Florian. You should be correct. It might call
> > mdiobus_unregister() and mdiobus_free() twice, once inside the dsa
> > code and another one by the devm (if I understood how devm functions
> > work).
> >
> > The issue is that the dsa switch is assuming that if slave_mii is
> > allocated and ds->ops->phy_read is defined, it has allocated the
> > slave_mii by itself and it should clean up the slave_mii during
> > teardown.
>
> Correct. Either the DSA core takes care of the mdiobus and uses the
> phy_read and phy_write ops, or the driver internally registers its own
> mdiobus, and phy_read and phy_write ops are not implemented. The core
> is not designed to mix those together.
>
> > if ds->ops->phy_read value should not tell if ds->slave_mii_bus should
> > be cleaned by the DSA switch.
> >
> > I would selfishly hope the correct one was the second option because
> > it would make my code much cleaner. If not, that's a complex issue to
> > solve without lots of duplications: realtek-smi drivers should not
> > have ds->ops->phy_read defined while realtek-mdio requires it. I'll
> > need to duplicate dsa_switch_ops for each subdriver only to unset
> > phy_read and also duplicate realtek_variant for each interface only to
> > reference that different dsa_switch_ops.
>
> One option would be to provide a dummy mdiobus driver for
> realtek-mdio, which simply passes the access through to the existing
> MDIO bus.
>
>      Andrew

Ok, thanks for the clarification, Andrew. In the end, I simply
duplicated ds_ops and wrote a wrap funcion.
Much less painful than I anticipated.

Should I submit a patch to make dsa work like this then?

dsa_switch_setup() {
        ....
        ds->ops->setup()
        ....
        if (ds->ops->phy_read) {
              if (ds->slave_mii_bus)
                    error("ds->ops->phy_read is set, I should be the
one allocating ds->slave_mii_bus!")
              ...allocate and register ds->slave_mii_bus...
        }
}

I think it is better to fail when there is an invalid setup than to
expect the dsa driver to behave correctly.

Regards,

Luiz