netdev - Re: [net-next: PATCH 08/12] ACPI: scan: prevent double enumeration of MDIO bus children

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Date:   Wed, 22 Jun 2022 18:21:31 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Andrew Lunn <andrew@...n.ch>, Marcin Wojtas <mw@...ihalf.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Len Brown <lenb@...nel.org>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        David Miller <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Grzegorz Bernacki <gjb@...ihalf.com>,
        Grzegorz Jaszczyk <jaz@...ihalf.com>,
        Tomasz Nowicki <tn@...ihalf.com>,
        Samer El-Haj-Mahmoud <Samer.El-Haj-Mahmoud@....com>,
        upstream@...ihalf.com
Subject: Re: [net-next: PATCH 08/12] ACPI: scan: prevent double enumeration of
 MDIO bus children

On Wed, Jun 22, 2022 at 6:12 PM Florian Fainelli <f.fainelli@...il.com> wrote:
>
> On 6/22/22 05:05, Rafael J. Wysocki wrote:
> > On Mon, Jun 20, 2022 at 9:08 PM Andrew Lunn <andrew@...n.ch> wrote:
> >>
> >> On Mon, Jun 20, 2022 at 05:02:21PM +0200, Marcin Wojtas wrote:
> >>> The MDIO bus is responsible for probing and registering its respective
> >>> children, such as PHYs or other kind of devices.
> >>>
> >>> It is required that ACPI scan code should not enumerate such
> >>> devices, leaving this task for the generic MDIO bus routines,
> >>> which are initiated by the controller driver.
> >>
> >> I suppose the question is, should you ignore the ACPI way of doing
> >> things, or embrace the ACPI way?
> >
> > What do you mean by "the ACPI way"?
> >
> >> At least please add a comment why the ACPI way is wrong, despite this
> >> being an ACPI binding.
> >
> > The question really is whether or not it is desirable to create
> > platform devices for all of the objects found in the ACPI tables that
> > correspond to the devices on the MDIO bus.
>
> If we have devices hanging off a MDIO bus then they are mdio_device (and
> possibly a more specialized object with the phy_device which does embedd
> a mdio_device object), not platform devices, since MDIO is a bus in itself.

Well, that's what I'm saying.

And when the ACPI subsystem finds those device objects present in the
ACPI tables, the mdio_device things have not been created yet and it
doesn't know which ACPI device object will correspond to mdio_device
eventually unless it is told about that somehow.  One way of doing
that is to use a list of device IDs in the kernel.  The other is to
have the firmware tell it about that which is what we are discussing.