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Date:   Thu, 22 Jun 2023 17:36:40 +0200
From:   Andrew Lunn <andrew@lunn.ch>
To:     Florian Fainelli <florian.fainelli@broadcom.com>
Cc:     netdev@vger.kernel.org, hkallweit1@gmail.com, ansuelsmth@gmail.com,
        rmk+kernel@armlinux.org.uk, Doug Berger <opendmb@gmail.com>,
        Broadcom internal kernel review list 
        <bcm-kernel-feedback-list@broadcom.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH net] net: bcmgenet: Ensure MDIO unregistration has clocks
 enabled
Message-ID: <533872e1-b323-4bca-aacc-4d3cfbed53bd@lunn.ch>
References: <20230622103107.1760280-1-florian.fainelli@broadcom.com>
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On Thu, Jun 22, 2023 at 03:31:07AM -0700, Florian Fainelli wrote:
> With support for Ethernet PHY LEDs having been added, while
> unregistering a MDIO bus and its child device liks PHYs there may be
> "late" accesses to the MDIO bus. One typical use case is setting the PHY
> LEDs brightness to OFF for instance.
> 
> We need to ensure that the MDIO bus controller remains entirely
> functional since it runs off the main GENET adapter clock.

So this clock is enabled in bcmgenet_open() and disabled in
bcmgenet_close(). The assumption being, the MDIO bus is only used when
the interface is up.

How does this work when there is an MDIO based switch attached? I had
similar problems with the FEC and mv88e6xxx. DSA would try to talk to
the switch with the master interface down, and MDIO would time out. I
needed to add runtime PM support to the MDIO bus ops.

       Andrew