linux-kernel - Re: [PATCH net-next v1 3/3] net: phy: micrel: Fix forced link mode for KSZ886X switches

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Message-ID: <20231011142526.GA3306548@pengutronix.de>
Date:   Wed, 11 Oct 2023 16:25:26 +0200
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Alexander Stein <alexander.stein@...tq-group.com>
Cc:     Woojung Huh <woojung.huh@...rochip.com>,
        UNGLinuxDriver@...rochip.com, Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Heiner Kallweit <hkallweit1@...il.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel@...gutronix.de,
        Russell King <linux@...linux.org.uk>
Subject: Re: [PATCH net-next v1 3/3] net: phy: micrel: Fix forced link mode
 for KSZ886X switches

Hi Alexander,

thank you for review!

On Wed, Oct 11, 2023 at 03:29:49PM +0200, Alexander Stein wrote:
> Hi Oleksij,
> 
> Am Mittwoch, 11. Oktober 2023, 14:38:56 CEST schrieb Oleksij Rempel:
> > Address a link speed detection issue in KSZ886X PHY driver when in
> > forced link mode. Previously, link partners like "ASIX AX88772B"
> > with KSZ8873 could fall back to 10Mbit instead of configured 100Mbit.
> > 
> > The issue arises as KSZ886X PHY continues sending Fast Link Pulses (FLPs)
> > even with autonegotiation off, misleading link partners in autoneg mode,
> > leading to incorrect link speed detection.
> > 
> > Now, when autonegotiation is disabled, the driver sets the link state
> > forcefully using KSZ886X_CTRL_FORCE_LINK bit. This action, beyond just
> > disabling autonegotiation, makes the PHY state more reliably detected by
> > link partners using parallel detection, thus fixing the link speed
> > misconfiguration.
> > 
> > With autonegotiation enabled, link state is not forced, allowing proper
> > autonegotiation process participation.
> > 
> > Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
> > ---
> >  drivers/net/phy/micrel.c | 32 +++++++++++++++++++++++++++++---
> >  1 file changed, 29 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/net/phy/micrel.c b/drivers/net/phy/micrel.c
> > index 927d3d54658e..12f093aed4ff 100644
> > --- a/drivers/net/phy/micrel.c
> > +++ b/drivers/net/phy/micrel.c
> > @@ -1729,9 +1729,35 @@ static int ksz886x_config_aneg(struct phy_device
> > *phydev) {
> >  	int ret;
> > 
> > -	ret = genphy_config_aneg(phydev);
> > -	if (ret)
> > -		return ret;
> > +	if (phydev->autoneg != AUTONEG_ENABLE) {
> > +		ret = genphy_setup_forced(phydev);
> > +		if (ret)
> > +			return ret;
> > +
> > +		/* When autonegotation is disabled, we need to manually 
> force
> > +		 * the link state. If we don't do this, the PHY will keep
> > +		 * sending Fast Link Pulses (FLPs) which are part of the
> > +		 * autonegotiation process. This is not desired when
> > +		 * autonegotiation is off.
> > +		 */
> > +		ret = phy_set_bits(phydev, MII_KSZPHY_CTRL,
> > +				   KSZ886X_CTRL_FORCE_LINK);
> > +		if (ret)
> > +			return ret;
> > +	} else {
> > +		/* Make sure, the link state is not forced.
> > +		 * Otherwise, the PHY we create a link by skipping the
> 
> PHY will create?
> 
> > +		 * autonegotiation process.
> > +		 */
> > +		ret = phy_clear_bits(phydev, MII_KSZPHY_CTRL,
> > +				     KSZ886X_CTRL_FORCE_LINK);
> > +		if (ret)
> > +			return ret;
> 
> Isn't this call to phy_clear_bits() a fix for autonegotiation mode? This 
> should be a separate patch then.

First time this bit is set by this patch, I assume this problem would
not exist without fixed link fix.

Regards,
Oleksij
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