netdev - Re: [PATCH net] net: phy: dp83869: Set auto mdix bit for forced 100Base-Tx mode

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Message-ID: <aYyDkaynWEm-WJdg@shell.armlinux.org.uk>
Date: Wed, 11 Feb 2026 13:26:41 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Meghana Malladi <m-malladi@...com>
Cc: pabeni@...hat.com, kuba@...nel.org, edumazet@...gle.com,
	davem@...emloft.net, hkallweit1@...il.com, andrew@...n.ch,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org, srk@...com,
	Vignesh Raghavendra <vigneshr@...com>,
	Roger Quadros <rogerq@...nel.org>, danishanwar@...com
Subject: Re: [PATCH net] net: phy: dp83869: Set auto mdix bit for forced
 100Base-Tx mode

On Wed, Feb 11, 2026 at 06:40:32PM +0530, Meghana Malladi wrote:
> When using DP83869 in force 100Base-Tx mode, the PHY is required
> to have robust Auto-MDIX feature enabled from register 1Eh.
> Refer to 7.4.1.2 100BASE-TX section in the TRM [1] for more details.
> 
> [1]: https://www.ti.com/lit/ds/symlink/dp83869hm.pdf
> Signed-off-by: Meghana Malladi <m-malladi@...com>
> ---
>  drivers/net/phy/dp83869.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/drivers/net/phy/dp83869.c b/drivers/net/phy/dp83869.c
> index 1f381d7b13ff..70d759c45c6a 100644
> --- a/drivers/net/phy/dp83869.c
> +++ b/drivers/net/phy/dp83869.c
> @@ -110,6 +110,7 @@
>  
>  /* CFG4 bits */
>  #define DP83869_INT_OE	BIT(7)
> +#define DP83869_CFG4_ENABLE_AUTO_MDIX_100FD	BIT(9)
>  
>  /* OP MODE */
>  #define DP83869_OP_MODE_MII			BIT(5)
> @@ -900,6 +901,23 @@ static int dp83869_phy_reset(struct phy_device *phydev)
>  	return dp83869_config_init(phydev);
>  }
>  
> +static void dp83869_link_change_notify(struct phy_device *phydev)
> +{
> +	int cfg4;
> +
> +	/* When using DP83869 in force 100Base-Tx mode, the PHY is required
> +	 * to have robust Auto-MDIX feature enabled
> +	 */
> +	if (phydev->autoneg == AUTONEG_DISABLE &&
> +	    phydev->speed == SPEED_100 &&
> +	    phydev->duplex == DUPLEX_FULL) {
> +		cfg4 = phy_read(phydev, DP83869_CFG4);
> +		if (cfg4 >= 0) {
> +			cfg4 |= DP83869_CFG4_ENABLE_AUTO_MDIX_100FD;
> +			phy_write(phydev, DP83869_CFG4, cfg4);
> +		}
> +	}

Shouldn't this kind of configuration be done via .config_aneg() ?

-- 
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