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Date:   Fri, 1 Jul 2022 11:13:40 +0200
From:   Andrew Lunn <andrew@lunn.ch>
To:     Radhey Shyam Pandey <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.com
Subject: Re: [PATCH net-next v2] net: macb: In shared MDIO usecase make MDIO
 producer ethernet node to probe first
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References: <1656618906-29881-1-git-send-email-radhey.shyam.pandey@amd.com>
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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.

     Andrew