netdev - Re: [PATCH net-next v2] net: macb: In shared MDIO usecase make MDIO producer ethernet node to probe first

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Message-ID: <CAGETcx_BUR3EPDLgp9v0Uk9N=8BtYRjFyhpJTQa9kEMHtkgdwQ@mail.gmail.com>
Date:   Tue, 5 Jul 2022 11:57:32 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     "Pandey, Radhey Shyam" <radhey.shyam.pandey@....com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        "nicolas.ferre@...rochip.com" <nicolas.ferre@...rochip.com>,
        "claudiu.beznea@...rochip.com" <claudiu.beznea@...rochip.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "hkallweit1@...il.com" <hkallweit1@...il.com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "rafael@...nel.org" <rafael@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "git (AMD-Xilinx)" <git@....com>
Subject: Re: [PATCH net-next v2] net: macb: In shared MDIO usecase make MDIO
 producer ethernet node to probe first

On Tue, Jul 5, 2022 at 11:49 AM Pandey, Radhey Shyam
<radhey.shyam.pandey@....com> wrote:
>
> > -----Original Message-----
> > From: Andrew Lunn <andrew@...n.ch>
> > Sent: Friday, July 1, 2022 2:44 PM
> > To: Pandey, Radhey Shyam <radhey.shyam.pandey@....com>
> > Cc: nicolas.ferre@...rochip.com; claudiu.beznea@...rochip.com;
> > davem@...emloft.net; edumazet@...gle.com; kuba@...nel.org;
> > pabeni@...hat.com; hkallweit1@...il.com; linux@...linux.org.uk;
> > gregkh@...uxfoundation.org; rafael@...nel.org; saravanak@...gle.com;
> > netdev@...r.kernel.org; linux-kernel@...r.kernel.org; git (AMD-Xilinx)
> > <git@....com>
> > Subject: Re: [PATCH net-next v2] net: macb: In shared MDIO usecase make
> > MDIO producer ethernet node to probe first
> >
> > 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 first.
> > > 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.
> >
> > I don't think there is anything specific to MACB here. There are Freescale
> > boards which have an MDIO bus shared by two interfaces etc.
> >
> > Please try to solve this in a generic way, not specific to one MAC and MDIO
> > 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?
>
> 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
> MDIO producer platform device is probed. If not, defer MDIO consumer
> MDIO bus registration.

Radhey,

I think Andrew added me because he's pointing you towards fw_devlink.

Andrew,

I have intentionally not added phy-handle support to fw_devlink
because it would also prevent the generic driver from binding/cause
issues with DSA. I have some high level ideas on fixing that but
haven't gotten around to it yet.

-Saravana