Re: [PATCH net 2/2] net: stmmac: qcom-ethqos: advertise supported SerDes interfaces

[Mohd Ayaan Anwar]

On Wed, Sep 16, 2026 at 08:39:50PM +1000, Thomas Karpiniec wrote:
> From: Thomas Karpiniec <tom@xxxxxxxx>
> 
> With a QCA8081 PHY and phy-mode = "2500base-x", stmmac reports only
> 2500BASE-X in phylink's supported_interfaces. Phylink consequently removes
> 10/100/1000BASE-T modes from the PHY's advertisement, preventing a link
> with a gigabit switch.
> 
> The QCA8081 uses SGMII for lower copper speeds and 2500BASE-X for 2.5Gbps.
> ETHQOS already reconfigures the SerDes in ethqos_mac_finish_serdes() when
> the PHY changes interface, but does not advertise this capability.
> 
> Provide a get_interfaces() callback for serial interfaces. Add SGMII and
> 2500BASE-X when the SerDes validates them, allowing phylink to retain the
> corresponding copper link modes. Leave the existing stmmac fallback to
> the firmware interface in place when no interfaces are reported. RGMII
> configurations are unchanged.
> 
> Fixes: 61e9be0efbe8 ("net: stmmac: qcom-ethqos: add support for 2.5G BASEX mode")
> Cc: stable@xxxxxxxxxxxxxxx # 7.1+
> Assisted-by: LLM sparse
> Signed-off-by: Thomas Karpiniec <tom@xxxxxxxx>
> ---
>  .../stmicro/stmmac/dwmac-qcom-ethqos.c        | 22 +++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c b/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c
> index ac7d6d3e205a..3493e090f1a8 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac-qcom-ethqos.c
> @@ -1,6 +1,7 @@
>  // SPDX-License-Identifier: GPL-2.0
>  // Copyright (c) 2018-19, Linaro Limited
>  
> +#include <linux/bitops.h>
>  #include <linux/module.h>
>  #include <linux/of.h>
>  #include <linux/of_net.h>
> @@ -564,6 +565,26 @@ static void ethqos_pcs_set_inband(struct qcom_ethqos *ethqos, bool enable)
>  	stmmac_pcs_ctrl_ane(priv, enable, 0);
>  }
>  
> +static void ethqos_get_interfaces_serdes(struct stmmac_priv *priv, void *bsp_priv,
> +					 unsigned long *interfaces)
> +{
> +	struct qcom_ethqos *ethqos = bsp_priv;
> +
> +	if (!ethqos->serdes_phy)
> +		return;
> +
> +	/* PHYs such as QCA8081 switch between SGMII and 2500BASE-X with
> +	 * the negotiated copper speed. mac_finish reconfigures the SerDes
> +	 * accordingly; let phylink validate all modes that path supports.
> +	 */
> +	if (!phy_validate(ethqos->serdes_phy, PHY_MODE_ETHERNET,
> +			  PHY_INTERFACE_MODE_SGMII, NULL))
> +		__set_bit(PHY_INTERFACE_MODE_SGMII, interfaces);
> +	if (!phy_validate(ethqos->serdes_phy, PHY_MODE_ETHERNET,
> +			  PHY_INTERFACE_MODE_2500BASEX, NULL))
> +		__set_bit(PHY_INTERFACE_MODE_2500BASEX, interfaces);
> +}
> +

So, I had proposed this exact change a while back:
https://lore.kernel.org/netdev/aMgootkPQ%2FGcdiXX@xxxxxxxxxxxxxxxx/

As Russell noted, this behaviour is due to the messed-up integrated
PCS support in STMMAC/QCOM-ETHQOS.

I would defer to him for this if he's around.

	Ayaan