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Date:   Fri, 13 Oct 2023 17:04:49 +0100
From:   "Russell King (Oracle)" <linux@armlinux.org.uk>
To:     Alexander Stein <alexander.stein@ew.tq-group.com>
Cc:     Woojung Huh <woojung.huh@microchip.com>,
        UNGLinuxDriver@microchip.com, Andrew Lunn <andrew@lunn.ch>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Vladimir Oltean <olteanv@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Heiner Kallweit <hkallweit1@gmail.com>,
        Oleksij Rempel <o.rempel@pengutronix.de>,
        kernel@pengutronix.de, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org
Subject: Re: [PATCH net-next v1 3/3] net: phy: micrel: Fix forced link mode
 for KSZ886X switches
Message-ID: <ZSlqoR8PGPQQw/aA@shell.armlinux.org.uk>
References: <20231011123856.1443308-1-o.rempel@pengutronix.de>
 <20231011123856.1443308-3-o.rempel@pengutronix.de>
 <3767760.kQq0lBPeGt@steina-w>
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Sender: Russell King (Oracle) <linux@armlinux.org.uk>
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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:
> > +	if (phydev->autoneg != AUTONEG_ENABLE) {
> > +		ret = genphy_setup_forced(phydev);
> > +		if (ret)
> > +			return ret;
> > +
...
> > +		ret = phy_set_bits(phydev, MII_KSZPHY_CTRL,
> > +				   KSZ886X_CTRL_FORCE_LINK);
> > +		if (ret)
> > +			return ret;
> > +	} else {
...
> > +		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.

No, I don't think that is the case. Compare the two paths above, noting
that patch 1 introduces the definition for KSZ886X_CTRL_FORCE_LINK.

If autoneg is disabled, then this bit is then set, which forces the
link. Clearly, if autoneg is then re-enabled, this bit has to be
cleared to allow the effects of the autoneg-disabled path to be undone.

So both of these, the phy_set_bits() and the phy_clear_bits() belong in
the same patch. Splitting them up, so we introduce phy_set_bits() first
will create a regression - which we don't want.

These two belong logically together.

What does concern me, however, is that the autoneg-disabled path avoids
calling genphy_setup_master_slave(), and since establishing which end
of the link is part of the fundamentals of a 1000base-T link, I wonder
whether both paths should still call genphy_config_aneg().

Apart from that, I think the patch is otherwise fine.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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