linux-kernel - Re: [PATCH net] net: phy: fix duplex out of sync problem while changing settings

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Date:   Mon, 1 Nov 2021 22:37:28 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Zhang Changzhong <zhangchangzhong@...wei.com>,
        Andrew Lunn <andrew@...n.ch>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: phy: fix duplex out of sync problem while
 changing settings

On 01.11.2021 10:44, Zhang Changzhong wrote:
> Before commit 2bd229df5e2e ("net: phy: remove state PHY_FORCING") if
> phy_ethtool_ksettings_set() is called with autoneg off, phy_start_aneg()
> will set phydev->state to PHY_FORCING, so adjust_link will always be
> called.
> 
> But after that commit, if phy_ethtool_ksettings_set() changes the local
> link from 10Mbps/Half to 10Mbps/Full when the link partner is
> 10Mbps/Full, phy_check_link_status() will not trigger the link change,
> because phydev->link and phydev->state has not changed. This will causes
> the duplex of the PHY and MAC to be out of sync.
> 
> Fix it by re-adding the PHY_FORCING state to force adjust_link to be
> called in fixed mode.
> 
> Fixes: 2bd229df5e2e ("net: phy: remove state PHY_FORCING")
> Signed-off-by: Zhang Changzhong <zhangchangzhong@...wei.com>
> ---
>  drivers/net/phy/phy.c | 10 ++++++++--
>  include/linux/phy.h   |  6 ++++++
>  2 files changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/phy/phy.c b/drivers/net/phy/phy.c
> index a3bfb15..b114f15 100644
> --- a/drivers/net/phy/phy.c
> +++ b/drivers/net/phy/phy.c
> @@ -49,6 +49,7 @@ static const char *phy_state_to_str(enum phy_state st)
>  	PHY_STATE_STR(UP)
>  	PHY_STATE_STR(RUNNING)
>  	PHY_STATE_STR(NOLINK)
> +	PHY_STATE_STR(FORCING)
>  	PHY_STATE_STR(CABLETEST)
>  	PHY_STATE_STR(HALTED)
>  	}
> @@ -724,8 +725,12 @@ static int _phy_start_aneg(struct phy_device *phydev)
>  	if (err < 0)
>  		return err;
>  
> -	if (phy_is_started(phydev))
> -		err = phy_check_link_status(phydev);
> +	if (phy_is_started(phydev)) {
> +		if (phydev->autoneg == AUTONEG_ENABLE)
> +			err = phy_check_link_status(phydev);
> +		else
> +			phydev->state = PHY_FORCING;
> +	}
>  
>  	return err;
>  }
> @@ -1120,6 +1125,7 @@ void phy_state_machine(struct work_struct *work)
>  		needs_aneg = true;
>  
>  		break;
> +	case PHY_FORCING:
>  	case PHY_NOLINK:
>  	case PHY_RUNNING:
>  		err = phy_check_link_status(phydev);
> diff --git a/include/linux/phy.h b/include/linux/phy.h
> index 736e1d1..e639729 100644
> --- a/include/linux/phy.h
> +++ b/include/linux/phy.h
> @@ -446,6 +446,11 @@ struct phy_device *mdiobus_scan(struct mii_bus *bus, int addr);
>   * - irq or timer will set @PHY_NOLINK if link goes down
>   * - phy_stop moves to @PHY_HALTED
>   *
> + * @PHY_FORCING: PHY is being configured with forced settings.
> + * - if link is up, move to @PHY_RUNNING
> + * - if link is down, move to @PHY_NOLINK
> + * - phy_stop moves to @PHY_HALTED
> + *
>   * @PHY_CABLETEST: PHY is performing a cable test. Packet reception/sending
>   * is not expected to work, carrier will be indicated as down. PHY will be
>   * poll once per second, or on interrupt for it current state.
> @@ -463,6 +468,7 @@ enum phy_state {
>  	PHY_UP,
>  	PHY_RUNNING,
>  	PHY_NOLINK,
> +	PHY_FORCING,
>  	PHY_CABLETEST,
>  };
>  
> 

I see your point, but the proposed fix may not be fully correct. You rely
on the phylib state machine, but there are drivers that use
phy_ethtool_ksettings_set() and some parts of phylib but not the phylib
state machine. One example is AMD xgbe.

Maybe the following is better, could you please give it a try?
By the way: With which MAC driver did you encounter the issue?


diff --git a/drivers/net/phy/phy.c b/drivers/net/phy/phy.c
index a3bfb156c..beb2b66da 100644
--- a/drivers/net/phy/phy.c
+++ b/drivers/net/phy/phy.c
@@ -815,7 +815,12 @@ int phy_ethtool_ksettings_set(struct phy_device *phydev,
 	phydev->mdix_ctrl = cmd->base.eth_tp_mdix_ctrl;
 
 	/* Restart the PHY */
-	_phy_start_aneg(phydev);
+	if (phy_is_started(phydev)) {
+		phydev->state = PHY_UP;
+		phy_trigger_machine(phydev);
+	} else {
+		_phy_start_aneg(phydev);
+	}
 
 	mutex_unlock(&phydev->lock);
 	return 0;
-- 
2.33.1