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Subject: Re: [RFC] net: phy: add shutdown hook to struct phy_driver
To:     Andrew Lunn <andrew@lunn.ch>,
        Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Cc:     Heiner Kallweit <hkallweit1@gmail.com>,
        Russell King <linux@armlinux.org.uk>,
        "David S. Miller" <davem@davemloft.net>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20200930174419.345cc9b4@xhacker.debian>
 <20200930190911.GU3996795@lunn.ch>
From:   Florian Fainelli <f.fainelli@gmail.com>
Message-ID: <bab6c68f-8ed7-26b7-65ed-a65c7210e691@gmail.com>
Date:   Wed, 30 Sep 2020 13:07:19 -0700
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On 9/30/2020 12:09 PM, Andrew Lunn wrote:
> On Wed, Sep 30, 2020 at 05:47:43PM +0800, Jisheng Zhang wrote:
>> Hi,
>>
>> A GE phy supports pad isolation which can save power in WOL mode. But once the
>> isolation is enabled, the MAC can't send/receive pkts to/from the phy because
>> the phy is "isolated". To make the PHY work normally, I need to move the
>> enabling isolation to suspend hook, so far so good. But the isolation isn't
>> enabled in system shutdown case, to support this, I want to add shutdown hook
>> to net phy_driver, then also enable the isolation in the shutdown hook. Is
>> there any elegant solution?
> 
>> Or we can break the assumption: ethernet can still send/receive pkts after
>> enabling WoL, no?
> 
> That is not an easy assumption to break. The MAC might be doing WOL,
> so it needs to be able to receive packets.
> 
> What you might be able to assume is, if this PHY device has had WOL
> enabled, it can assume the MAC does not need to send/receive after
> suspend. The problem is, phy_suspend() will not call into the driver
> is WOL is enabled, so you have no idea when you can isolate the MAC
> from the PHY.
> 
> So adding a shutdown in mdio_driver_register() seems reasonable.  But
> you need to watch out for ordering. Is the MDIO bus driver still
> running?

If your Ethernet MAC controller implements a shutdown callback and that 
callback takes care of unregistering the network device which should 
also ensure that phy_disconnect() gets called, then your PHY's suspend 
function will be called.
-- 
Florian