netdev - Re: [PATCH] of: of_mdio: Handle properties for non-phy mdio devices

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Date:   Wed, 17 Feb 2021 08:57:13 +1000
From:   Nathan Rossi <nathan@...hanrossi.com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>, netdev@...r.kernel.org,
        Nathan Rossi <nathan.rossi@...i.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH] of: of_mdio: Handle properties for non-phy mdio devices

On Wed, 17 Feb 2021 at 03:50, Florian Fainelli <f.fainelli@...il.com> wrote:
>
>
>
> On 2/16/2021 5:06 AM, Andrew Lunn wrote:
> > On Mon, Feb 15, 2021 at 07:02:18AM +0000, Nathan Rossi wrote:
> >> From: Nathan Rossi <nathan.rossi@...i.com>
> >>
> >> The documentation for MDIO bindings describes the "broken-turn-around",
> >> "reset-assert-us", and "reset-deassert-us" properties such that any MDIO
> >> device can define them. Other MDIO devices may require these properties
> >> in order to correctly function on the MDIO bus.
> >>
> >> Enable the parsing and configuration associated with these properties by
> >> moving the associated OF parsing to a common function
> >> of_mdiobus_child_parse and use it to apply these properties for both
> >> PHYs and other MDIO devices.
> >
> > Hi Nathan
> >
> > What device are you using this with?
> >
> > The Marvell Switch driver does its own GPIO reset handling. It has a
> > better idea when a hardware reset should be applied than what the
> > phylib core has. It will also poll the EEPROM busy bit after a
> > reset. How long a pause you need after the reset depends on how full
> > the EEPROM is.
> >
> > And i've never had problems with broken-turn-around with Marvell
> > switches.
>
> The patch does make sense though, Broadcom 53125 switches have a broken
> turn around and are mdio_device instances, the broken behavior may not
> show up with all MDIO controllers used to interface though. For the

Yes the reason we needed this change was to enable broken turn around,
specifically with a Marvell 88E6390.

> reset, I would agree with you this is better delegated to the switch
> driver, given that unlike PHY devices, we have no need to know the
> mdio_device ID prior to binding the device and the driver together.
>
> >
> > Given the complexity of an Ethernet switch, it is probably better if
> > it handles its own reset.

We are not using the reset assert, I included this as part of the
change to match the existing phy parsing behavior. I can update this
change to only handle broken turn around, or is it also preferred that
broken turn around is handled by the e.g. switch driver?

Thanks,
Nathan