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

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Message-ID: <0499fc01-fce3-26c7-8b42-64788b8bf47b@gmail.com>
Date:   Thu, 29 Nov 2018 23:47:38 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>
Cc:     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

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.

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.

>  	phy_start_machine(phydev);
>  
>