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From:   Marcin Wojtas <mw@semihalf.com>
Date:   Wed, 22 Jun 2022 17:05:30 +0200
Message-ID: <CAPv3WKcpKYV2OQuy3KMKW6u09Rp2-d422WspB6uo6ta=mvhN8Q@mail.gmail.com>
Subject: Re: [net-next: PATCH 08/12] ACPI: scan: prevent double enumeration of
 MDIO bus children
To:     "Rafael J. Wysocki" <rafael@kernel.org>
Cc:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
        netdev <netdev@vger.kernel.org>, Len Brown <lenb@kernel.org>,
        Andrew Lunn <andrew@lunn.ch>,
        Vivien Didelot <vivien.didelot@gmail.com>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Vladimir Oltean <olteanv@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Russell King - ARM Linux <linux@armlinux.org.uk>,
        Heiner Kallweit <hkallweit1@gmail.com>,
        Grzegorz Bernacki <gjb@semihalf.com>,
        Grzegorz Jaszczyk <jaz@semihalf.com>,
        Tomasz Nowicki <tn@semihalf.com>,
        Samer El-Haj-Mahmoud <Samer.El-Haj-Mahmoud@arm.com>,
        upstream@semihalf.com
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=C5=9Br., 22 cze 2022 o 14:09 Rafael J. Wysocki <rafael@kernel.org> napisa=
=C5=82(a):
>
> On Tue, Jun 21, 2022 at 1:05 AM Marcin Wojtas <mw@semihalf.com> wrote:
> >
> > pon., 20 cze 2022 o 19:53 Andy Shevchenko
> > <andriy.shevchenko@linux.intel.com> napisa=C5=82(a):
> > >
> > > On Mon, Jun 20, 2022 at 05:02:21PM +0200, Marcin Wojtas wrote:
> > > > The MDIO bus is responsible for probing and registering its respect=
ive
> > > > 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.
> > > >
> > > > This patch prevents unwanted enumeration of the devices by setting
> > > > 'enumeration_by_parent' flag, depending on whether their parent
> > > > device is a member of a known list of MDIO controllers. For now,
> > > > the Marvell MDIO controllers' IDs are added.
> > >
> > > This flag is used for serial buses that are not self-discoverable. No=
t sure
> > > about MDIO, but the current usage has a relation to the _CRS. Have yo=
u
> > > considered to propose the MdioSerialBus() resource type to ACPI speci=
fication?
> > >
> >
> > Indeed, one of the cases checked in the
> > acpi_device_enumeration_by_parent() is checking _CRS (of the bus child
> > device) for being of the serial bus type. Currently I see
> > I2C/SPI/UARTSerialBus resource descriptors in the specification. Since
> > MDIO doesn't seem to require any special description macros like the
> > mentioned ones (for instance see I2CSerialBusV2 [1]), Based on
> > example: dfda4492322ed ("ACPI / scan: Do not enumerate Indirect IO
> > host children"), I thought of similar one perhaps being applicable.
> >
> > Maybe there is some different, more proper solution, I'd be happy to
> > hear from the ACPI Maintainers.
> >
> > [1] https://uefi.org/specs/ACPI/6.4/19_ASL_Reference/ACPI_Source_Langua=
ge_Reference.html?highlight=3Di2cserialbus#i2cserialbusterm
>
> Well, the approach based on lists of device IDs is not scalable and
> generally used as the last resort one.
>
> It would be a lot better to have a way of representing connections to
> the MDIO bus as resources in _CRS.

Thank you for your input. I will submit a proposal for MDIOSerialBus
_CRS resource macro then.

Best regards,
Marcin