linux-kernel - Re: [PATCH net-next v2 3/3] net: phy: micrel: Fix forced link mode for KSZ886X switches

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Message-ID: <20231019094902.GB3632494@pengutronix.de>
Date:   Thu, 19 Oct 2023 11:49:02 +0200
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Woojung Huh <woojung.huh@...rochip.com>,
        UNGLinuxDriver@...rochip.com, Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...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>, kernel@...gutronix.de,
        linux-kernel@...r.kernel.org, Russell King <linux@...linux.org.uk>,
        netdev@...r.kernel.org,
        Alexander Stein <alexander.stein@...tq-group.com>
Subject: Re: [PATCH net-next v2 3/3] net: phy: micrel: Fix forced link mode
 for KSZ886X switches

Hi Vladimir,

On Fri, Oct 13, 2023 at 03:26:46PM +0300, Vladimir Oltean wrote:
> Hi Oleksij,
> 
> On Thu, Oct 12, 2023 at 08:55:02AM +0200, Oleksij Rempel wrote:
> > 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>
> > ---
> 
> Have you considered denying "ethtool -s swpN autoneg off" in "net.git"
> (considering that it doesn't work properly), and re-enabling it in
> "net-next.git"?

Yes, but for ksz8 task I don't have budget to go this way.

> >  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..599ebf54fafe 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;
> 
> __genphy_config_aneg() will call genphy_setup_forced() as appropriate,
> and additionally it will resync the master-slave resolution to a forced
> value, if needed. So I think it's better to call genphy_config_aneg()
> from the common code path, and just use the "if (phydev->autoneg)" test
> to keep the vendor-specific register in sync with the autoneg setting.

ack. Will update it.

Regards,
Oleksij
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