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

[Andrew Lunn <andrew@lunn.ch>]

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