netdev - Re: [RFC] net: phy: add shutdown hook to struct phy

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Date:   Wed, 30 Sep 2020 22:11:35 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Jisheng Zhang <Jisheng.Zhang@...aptics.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC] net: phy: add shutdown hook to struct phy_driver

On Wed, Sep 30, 2020 at 01:07:19PM -0700, Florian Fainelli wrote:
> 
> 
> 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.

Hi Florian

I could be missing something here, but:

phy_suspend does not call into the PHY driver if WOL is enabled. So
Jisheng needs a way to tell the PHY it should isolate itself from the
MAC, and suspend is not that.

     Andrew