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

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Message-ID: <20230830101813.GG31399@pengutronix.de>
Date:   Wed, 30 Aug 2023 12:18:13 +0200
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Lukasz Majewski <lukma@...x.de>
Cc:     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,
        Russell King <linux@...linux.org.uk>,
        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 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);
   else
      /* lots of other comments */
      linkmode_and(phydev->supported_eee, phydev->supported,
                   PHY_EEE_CAP1_FEATURES);

On the switch driver side i would expect something like this:
ksz_get_phy_flags(struct dsa_switch *ds, int port)

       swtich (dev->chip_id)
       case KSZ8830_CHIP_ID:
         ....
         break;
       case KSZ9477_CHIP_ID:
         return MICREL_NO_EEE;


Regards,
Oleksij
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