netdev - Re: [PATCH net-next v1 3/3] net: phy: micrel: Fix forced link mode for KSZ886X switches

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Date: Fri, 13 Oct 2023 17:48:00 +0200
From: Simon Horman <horms@...nel.org>
To: Oleksij Rempel <o.rempel@...gutronix.de>
Cc: Woojung Huh <woojung.huh@...rochip.com>, UNGLinuxDriver@...rochip.com,
	Andrew Lunn <andrew@...n.ch>,
	Florian Fainelli <f.fainelli@...il.com>,
	Vladimir Oltean <olteanv@...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
Subject: Re: [PATCH net-next v1 3/3] net: phy: micrel: Fix forced link mode
 for KSZ886X switches

On Wed, Oct 11, 2023 at 02:38:56PM +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>
> ---
>  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..12f093aed4ff 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;
> +
> +		/* When autonegotation is disabled, we need to manually force

nit: autonegotiation

> +		 * the link state. If we don't do this, the PHY will keep
> +		 * sending Fast Link Pulses (FLPs) which are part of the
> +		 * autonegotiation process. This is not desired when
> +		 * autonegotiation is off.
> +		 */

...