linux-kernel - Re: [PATCH net-next v2 2/3] net: ethernet: ti: am65-cpsw: fixup PHY mode for fixed RGMII TX delay

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Message-ID: <54d6cd05-65ef-4e1d-8041-3e4a2c50b443@ti.com>
Date: Thu, 26 Jun 2025 15:10:50 +0530
From: Siddharth Vadapalli <s-vadapalli@...com>
To: Matthias Schiffer <matthias.schiffer@...tq-group.com>
CC: Andrew Lunn <andrew+netdev@...n.ch>,
        "David S. Miller"
	<davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
	<kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Rob Herring
	<robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley
	<conor+dt@...nel.org>,
        Andy Whitcroft <apw@...onical.com>,
        Dwaipayan Ray
	<dwaipayanray1@...il.com>,
        Lukas Bulwahn <lukas.bulwahn@...il.com>,
        Joe
 Perches <joe@...ches.com>, Jonathan Corbet <corbet@....net>,
        Nishanth Menon
	<nm@...com>, Vignesh Raghavendra <vigneshr@...com>,
        Siddharth Vadapalli
	<s-vadapalli@...com>,
        Roger Quadros <rogerq@...nel.org>, Tero Kristo
	<kristo@...nel.org>,
        <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <netdev@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <linux@...tq-group.com>,
        Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Andrew Lunn <andrew@...n.ch>
Subject: Re: [PATCH net-next v2 2/3] net: ethernet: ti: am65-cpsw: fixup PHY
 mode for fixed RGMII TX delay

On Tue, Jun 24, 2025 at 12:53:33PM +0200, Matthias Schiffer wrote:

Hello Matthias,

> All am65-cpsw controllers have a fixed TX delay, so the PHY interface
> mode must be fixed up to account for this.
> 
> Modes that claim to a delay on the PCB can't actually work. Warn people
> to update their Device Trees if one of the unsupported modes is specified.
> 
> Signed-off-by: Matthias Schiffer <matthias.schiffer@...tq-group.com>
> Reviewed-by: Maxime Chevallier <maxime.chevallier@...tlin.com>
> Reviewed-by: Andrew Lunn <andrew@...n.ch>
> ---
>  drivers/net/ethernet/ti/am65-cpsw-nuss.c | 27 ++++++++++++++++++++++--
>  1 file changed, 25 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/ti/am65-cpsw-nuss.c b/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> index f20d1ff192efe..519757e618ad0 100644
> --- a/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> +++ b/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> @@ -2602,6 +2602,7 @@ static int am65_cpsw_nuss_init_slave_ports(struct am65_cpsw_common *common)
>  		return -ENOENT;
>  
>  	for_each_child_of_node(node, port_np) {
> +		phy_interface_t phy_if;
>  		struct am65_cpsw_port *port;
>  		u32 port_id;
>  
> @@ -2667,14 +2668,36 @@ static int am65_cpsw_nuss_init_slave_ports(struct am65_cpsw_common *common)
>  
>  		/* get phy/link info */
>  		port->slave.port_np = of_node_get(port_np);
> -		ret = of_get_phy_mode(port_np, &port->slave.phy_if);
> +		ret = of_get_phy_mode(port_np, &phy_if);
>  		if (ret) {
>  			dev_err(dev, "%pOF read phy-mode err %d\n",
>  				port_np, ret);
>  			goto of_node_put;
>  		}
>  
> -		ret = phy_set_mode_ext(port->slave.ifphy, PHY_MODE_ETHERNET, port->slave.phy_if);
> +		/* CPSW controllers supported by this driver have a fixed
> +		 * internal TX delay in RGMII mode. Fix up PHY mode to account
> +		 * for this and warn about Device Trees that claim to have a TX
> +		 * delay on the PCB.
> +		 */
> +		switch (phy_if) {
> +		case PHY_INTERFACE_MODE_RGMII_ID:
> +			phy_if = PHY_INTERFACE_MODE_RGMII_RXID;
> +			break;
> +		case PHY_INTERFACE_MODE_RGMII_TXID:
> +			phy_if = PHY_INTERFACE_MODE_RGMII;
> +			break;
> +		case PHY_INTERFACE_MODE_RGMII:
> +		case PHY_INTERFACE_MODE_RGMII_RXID:
> +			dev_warn(dev,
> +				 "RGMII mode without internal TX delay unsupported; please fix your Device Tree\n");

Existing users designed boards and enabled Ethernet functionality using
"rgmii-rxid" in the device-tree and implementing the PCB traces in a
way that they interpret "rgmii-rxid". So their (mis)interpretation of
it is being challenged by the series. While it is true that we are updating
the bindings and driver to move towards the correct definition, I believe that
the above message would cause confusion. Would it be alright to update it to
something similar to:

"Interpretation of RGMII delays has been corrected; no functional impact; please fix your Device Tree"

Regards,
Siddharth.