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From:   "Pandey, Radhey Shyam" <radhey.shyam.pandey@amd.com>
To:     Andrew Lunn <andrew@lunn.ch>
CC:     "nicolas.ferre@microchip.com" <nicolas.ferre@microchip.com>,
        "claudiu.beznea@microchip.com" <claudiu.beznea@microchip.com>,
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Subject: RE: [PATCH net-next v2] net: macb: In shared MDIO usecase make MDIO
 producer ethernet node to probe first
Thread-Topic: [PATCH net-next v2] net: macb: In shared MDIO usecase make MDIO
 producer ethernet node to probe first
Thread-Index: AQHYjLtb1TFGTzmc5Uq+BMzIcSbNRq1pPD4AgAbloJA=
Date:   Tue, 5 Jul 2022 18:49:06 +0000
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References: <1656618906-29881-1-git-send-email-radhey.shyam.pandey@amd.com>
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> -----Original Message-----
> From: Andrew Lunn <andrew@lunn.ch>
> Sent: Friday, July 1, 2022 2:44 PM
> To: Pandey, Radhey Shyam <radhey.shyam.pandey@amd.com>
> Cc: nicolas.ferre@microchip.com; claudiu.beznea@microchip.com;
> davem@davemloft.net; edumazet@google.com; kuba@kernel.org;
> pabeni@redhat.com; hkallweit1@gmail.com; linux@armlinux.org.uk;
> gregkh@linuxfoundation.org; rafael@kernel.org; saravanak@google.com;
> netdev@vger.kernel.org; linux-kernel@vger.kernel.org; git (AMD-Xilinx)
> <git@amd.com>
> Subject: Re: [PATCH net-next v2] net: macb: In shared MDIO usecase make
> MDIO producer ethernet node to probe first
>=20
> On Fri, Jul 01, 2022 at 01:25:06AM +0530, Radhey Shyam Pandey wrote:
> > In shared MDIO suspend/resume usecase for ex. with MDIO producer
> > (0xff0c0000) eth1 and MDIO consumer(0xff0b0000) eth0 there is a
> > constraint that ethernet interface(ff0c0000) MDIO bus producer has to
> > be resumed before the consumer ethernet interface(ff0b0000).
> >
> > However above constraint is not met when GEM0(ff0b0000) is resumed firs=
t.
> > There is phy_error on GEM0 and interface becomes non-functional on
> resume.
> >
> > suspend:
> > [ 46.477795] macb ff0c0000.ethernet eth1: Link is Down [ 46.483058]
> > macb ff0c0000.ethernet: gem-ptp-timer ptp clock unregistered.
> > [ 46.490097] macb ff0b0000.ethernet eth0: Link is Down [ 46.495298]
> > macb ff0b0000.ethernet: gem-ptp-timer ptp clock unregistered.
> >
> > resume:
> > [ 46.633840] macb ff0b0000.ethernet eth0: configuring for phy/sgmii
> > link mode macb_mdio_read -> pm_runtime_get_sync(GEM1) it return -
> EACCES error.
> >
> > The suspend/resume is dependent on probe order so to fix this
> > dependency ensure that MDIO producer ethernet node is always probed
> > first followed by MDIO consumer ethernet node.
> >
> > During MDIO registration find out if MDIO bus is shared and check if
> > MDIO producer platform node(traverse by 'phy-handle' property) is
> > bound. If not bound then defer the MDIO consumer ethernet node probe.
> > Doing it ensures that in suspend/resume MDIO producer is resumed
> > followed by MDIO consumer ethernet node.
>=20
> I don't think there is anything specific to MACB here. There are Freescal=
e
> boards which have an MDIO bus shared by two interfaces etc.
>=20
> Please try to solve this in a generic way, not specific to one MAC and MD=
IO
> combination.

Thanks for the review.  I want to get your thoughts on the outline of
the generic solution. Is the current approach fine and we can extend it
for all shared MDIO use cases/ or do we see any limitations?
=20
a) Figure out if the MDIO bus is shared.  (new binding or reuse existing)
b) If the MDIO bus is shared based on DT property then figure out if the=20
MDIO producer platform device is probed. If not, defer MDIO consumer
MDIO bus registration.

>=20
>      Andrew