netdev - Re: [PATCH net] net: dsa: bcm_sf2: Do not register slave MDIO bus with OF

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Date:   Mon, 6 Apr 2020 11:30:35 -0400
From:   Vivien Didelot <vivien.didelot@...il.com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
        Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] net: dsa: bcm_sf2: Do not register slave MDIO bus
 with OF

On Sat,  4 Apr 2020 14:35:17 -0700, Florian Fainelli <f.fainelli@...il.com> wrote:
> We were registering our slave MDIO bus with OF and doing so with
> assigning the newly created slave_mii_bus of_node to the master MDIO bus
> controller node. This is a bad thing to do for a number of reasons:
> 
> - we are completely lying about the slave MII bus is arranged and yet we
>   still want to control which MDIO devices it probes. It was attempted
>   before to play tricks with the bus_mask to perform that:
>   https://www.spinics.net/lists/netdev/msg429420.html but the approach
>   was rightfully rejected
> 
> - the device_node reference counting is messed up and we are effectively
>   doing a double probe on the devices we already probed using the
>   master, this messes up all resources reference counts (such as clocks)
> 
> The proper fix for this as indicated by David in his reply to the
> thread above is to use a platform data style registration so as to
> control exactly which devices we probe:
> https://www.spinics.net/lists/netdev/msg430083.html
> 
> By using mdiobus_register(), our slave_mii_bus->phy_mask value is used
> as intended, and all the PHY addresses that must be redirected towards
> our slave MDIO bus is happening while other addresses get redirected
> towards the master MDIO bus.
> 
> Fixes: 461cd1b03e32 ("net: dsa: bcm_sf2: Register our slave MDIO bus")
> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>

Reviewed-by: Vivien Didelot <vivien.didelot@...il.com>