linux-kernel - Re: [RFC PATCH net] net: phy: fix the issue that netif always links up after resuming

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Date:   Fri, 30 Nov 2018 13:37:39 +0900
From:   Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
To:     Heiner Kallweit <hkallweit1@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH net] net: phy: fix the issue that netif always links up after resuming

Hi Heiner Florian,

Thank you for your comments.

On Thu, 29 Nov 2018 16:37:48 -0800 <f.fainelli@...il.com> wrote:

> 
> 
> On 11/29/2018 2:47 PM, Heiner Kallweit wrote:
> > On 29.11.2018 09:12, Kunihiko Hayashi wrote:
> >> Even though the link is down before entering hibernation,
> >> there is an issue that the network interface always links up after resuming
> >> from hibernation.
> >>
> >> The phydev->state is PHY_READY before enabling the network interface, so
> >> the link is down. After resuming from hibernation, the phydev->state is
> >> forcibly set to PHY_UP in mdio_bus_phy_restore(), and the link becomes up.
> >>
> >> This patch expects to solve the issue by changing phydev->state to PHY_UP
> >> only when the link is up.
> >>
> >> Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
> >> ---
> >>  drivers/net/phy/phy_device.c | 6 ++++--
> >>  1 file changed, 4 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
> >> index ab33d17..d5bba0f 100644
> >> --- a/drivers/net/phy/phy_device.c
> >> +++ b/drivers/net/phy/phy_device.c
> >> @@ -309,8 +309,10 @@ static int mdio_bus_phy_restore(struct device *dev)
> >>  		return ret;
> >>  
> >>  	/* The PHY needs to renegotiate. */
> >> -	phydev->link = 0;
> >> -	phydev->state = PHY_UP;
> >> +	if (phydev->link) {
> >> +		phydev->link = 0;
> >> +		phydev->state = PHY_UP;
> >> +	}
> >>  
> > Thanks for reporting. I agree that it isn't right to unconditionally set
> > PHY_UP, because we don't know whether the PHY was started before
> > hibernation. However I don't think using phydev->link as criteria is
> > right. Example would be: PHY was started before hibernation, but w/o link.
> > In this case we want to set PHY_UP to start an aneg, because a cable may
> > have been plugged in whilst system was sleeping.

Indeed. I didn't consider the case that the PHY was started but a cable was
unplugged before hibernation.

> > So I think, similar to phy_stop_machine, we should use state >= UP and
> > state != HALTED as criteria, and also phy_start_machine() would need to
> > be called only if this criteria is met.
> > 
> > It may make sense to add a helper for checking whether PHY is in a
> > started state (>=UP && !=HALTED), because we need this in more than
> > one place.
> 
> Agreed, that would make sense.

I agree, too.
I'll try this in v2 patch that changes the PHY state to PHY_UP and calls
phy_start_machine(), only when the PHY was started before hibernation.
If I understand correctly, it will be like that:

	phydev->link = 0;
	if (phy_is_started(phydev)) {
		phydev->state = PHY_UP;
		phy_start_machine(phydev);
	}

Thank you,

---
Best Regards,
Kunihiko Hayashi