linux-kernel - Re: [PATCH 2/2] net: phy: Provide Module 4 KSZ9477 errata (DS80000754C)

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Message-ID: <ZO8l42ooy3PX1l8X@shell.armlinux.org.uk>
Date:   Wed, 30 Aug 2023 12:20:03 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Oleksij Rempel <o.rempel@...gutronix.de>
Cc:     Lukasz Majewski <lukma@...x.de>,
        Eric Dumazet <edumazet@...gle.com>,
        Andrew Lunn <andrew@...n.ch>, davem@...emloft.net,
        Woojung Huh <woojung.huh@...rochip.com>,
        Vladimir Oltean <olteanv@...il.com>, Tristram.Ha@...rochip.com,
        Florian Fainelli <f.fainelli@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, UNGLinuxDriver@...rochip.com,
        Heiner Kallweit <hkallweit1@...il.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] net: phy: Provide Module 4 KSZ9477 errata
 (DS80000754C)

On Wed, Aug 30, 2023 at 12:18:13PM +0200, Oleksij Rempel wrote:
> On Wed, Aug 30, 2023 at 11:21:19AM +0200, Lukasz Majewski wrote:
> > The KSZ9477 errata points out (in 'Module 4') the link up/down problem
> > when EEE (Energy Efficient Ethernet) is enabled in the device to which
> > the KSZ9477 tries to auto negotiate.
> > 
> > The suggested workaround is to clear advertisement of EEE for PHYs in
> > this chip driver.
> > 
> > Signed-off-by: Lukasz Majewski <lukma@...x.de>
> > ---
> >  drivers/net/phy/micrel.c | 31 ++++++++++++++++++++++++++++++-
> >  1 file changed, 30 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/net/phy/micrel.c b/drivers/net/phy/micrel.c
> > index 87b090ad2874..469dcd8a5711 100644
> > --- a/drivers/net/phy/micrel.c
> > +++ b/drivers/net/phy/micrel.c
> > @@ -1418,6 +1418,35 @@ static int ksz9131_get_features(struct phy_device *phydev)
> >  	return 0;
> >  }
> >  
> > +static int ksz9477_get_features(struct phy_device *phydev)
> > +{
> > +	__ETHTOOL_DECLARE_LINK_MODE_MASK(zero) = { 0, };
> > +	int ret;
> > +
> > +	ret = genphy_read_abilities(phydev);
> > +	if (ret)
> > +		return ret;
> > +
> > +	/* KSZ9477 Errata DS80000754C
> > +	 *
> > +	 * Module 4: Energy Efficient Ethernet (EEE) feature select must be
> > +	 * manually disabled
> > +	 *   The EEE feature is enabled by default, but it is not fully
> > +	 *   operational. It must be manually disabled through register
> > +	 *   controls. If not disabled, the PHY ports can auto-negotiate
> > +	 *   to enable EEE, and this feature can cause link drops when linked
> > +	 *   to another device supporting EEE.
> > +	 *
> > +	 *   Although, the KSZ9477 MMD register
> > +	 *   (MMD_DEVICE_ID_EEE_ADV.MMD_EEE_ADV) advertise that EEE is
> > +	 *   operational one needs to manualy clear them to follow the chip
> > +	 *   errata.
> > +	 */
> > +	linkmode_and(phydev->supported_eee, phydev->supported, zero);
> > +
> > +	return 0;
> > +}
> > +
> >  #define KSZ8873MLL_GLOBAL_CONTROL_4	0x06
> >  #define KSZ8873MLL_GLOBAL_CONTROL_4_DUPLEX	BIT(6)
> >  #define KSZ8873MLL_GLOBAL_CONTROL_4_SPEED	BIT(4)
> > @@ -4871,7 +4900,7 @@ static struct phy_driver ksphy_driver[] = {
> >  	.handle_interrupt = kszphy_handle_interrupt,
> >  	.suspend	= genphy_suspend,
> >  	.resume		= genphy_resume,
> > -	.get_features	= ksz9131_get_features,
> > +	.get_features	= ksz9477_get_features,
> 
> Sorry, i didn't described all details how to implement it.
> 
> This code will break EEE support for the KSZ8563R switch.
> 
> Please search for MICREL_KSZ8_P1_ERRATA in the kernel source.
> Then add new flag, for example MICREL_NO_EEE and use it in a similar
> way how MICREL_KSZ8_P1_ERRATA was set and used. With this
> implementation, first patch is not needed.
> 
> The code will be something like this:
>    if (dev_flags & MICREL_NO_EEE)
>       /* lots of comments */
>       linkmode_and(phydev->supported_eee, phydev->supported, zero);

I can't believe two people are writing code like this...

	linkmode_zero(phydev->supported_eee);

will work just as well.

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