It looks like the configuration of in-band AN only affects SGMII, and it
is always disabled for 2500Base-X. Adjust the reported capabilities
accordingly.

This is based on testing using OpenWrt on Zyxel XGS1010-12 rev A1 with
RTL8226-CG, and Zyxel XGS1210-12 rev B1 with RTL8221B-VB-CG. On these
devices, 2500Base-X in-band AN is known to work with some SFP modules
(containing an unknown PHY). However, with the built-in Realtek PHYs,
no auto-negotiation takes place, irrespective of the configuration of
the PHY.

Fixes: 10fbd71fc5f9b ("net: phy: realtek: implement configuring in-band an")
Signed-off-by: Jan Hoffmann <jan@3e8.eu>
---
 drivers/net/phy/realtek/realtek_main.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/phy/realtek/realtek_main.c b/drivers/net/phy/realtek/realtek_main.c
index 5a7f472bf58e..7b7a48e5082a 100644
--- a/drivers/net/phy/realtek/realtek_main.c
+++ b/drivers/net/phy/realtek/realtek_main.c
@@ -1429,6 +1429,7 @@ static unsigned int rtl822x_inband_caps(struct phy_device *phydev,
 {
 	switch (interface) {
 	case PHY_INTERFACE_MODE_2500BASEX:
+		return LINK_INBAND_DISABLE;
 	case PHY_INTERFACE_MODE_SGMII:
 		return LINK_INBAND_DISABLE | LINK_INBAND_ENABLE;
 	default:
-- 
2.52.0

On Tue, Jan 13, 2026 at 09:55:44PM +0100, Jan Hoffmann wrote:
> It looks like the configuration of in-band AN only affects SGMII, and it
> is always disabled for 2500Base-X. Adjust the reported capabilities
> accordingly.
> 
> This is based on testing using OpenWrt on Zyxel XGS1010-12 rev A1 with
> RTL8226-CG, and Zyxel XGS1210-12 rev B1 with RTL8221B-VB-CG. On these
> devices, 2500Base-X in-band AN is known to work with some SFP modules
> (containing an unknown PHY). However, with the built-in Realtek PHYs,
> no auto-negotiation takes place, irrespective of the configuration of
> the PHY.

This observation is aligned with the SFP quirk sfp_quirk_oem_2_5g()
which also disabled in-band AN for those 2.5G copper modules, some are
reportedly containing a RTL8221B-VB-CG PHY (the vendor and device ID
strings do *not* uniquely identify one design in this case,
unfortunately...)

> 
> Fixes: 10fbd71fc5f9b ("net: phy: realtek: implement configuring in-band an")
> Signed-off-by: Jan Hoffmann <jan@3e8.eu>

Reviewed-by: Daniel Golle <daniel@makrotopia.org>

> ---
>  drivers/net/phy/realtek/realtek_main.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/net/phy/realtek/realtek_main.c b/drivers/net/phy/realtek/realtek_main.c
> index 5a7f472bf58e..7b7a48e5082a 100644
> --- a/drivers/net/phy/realtek/realtek_main.c
> +++ b/drivers/net/phy/realtek/realtek_main.c
> @@ -1429,6 +1429,7 @@ static unsigned int rtl822x_inband_caps(struct phy_device *phydev,
>  {
>  	switch (interface) {
>  	case PHY_INTERFACE_MODE_2500BASEX:
> +		return LINK_INBAND_DISABLE;
>  	case PHY_INTERFACE_MODE_SGMII:
>  		return LINK_INBAND_DISABLE | LINK_INBAND_ENABLE;
>  	default:
> -- 
> 2.52.0
>