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

From: Michal Swiatkowski <[email-masked]>
Date: Wed, 30 Aug 2023 11:48:31 +0200

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 <[email-masked]>
Hi,

As the net is target you should add fixes tag which the commit that your
changes is fixing (workarounding :) )

> ---
>  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, };
= { 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,
>  } };
>  
>  module_phy_driver(ksphy_driver);
> -- 
> 2.20.1
>