AW: pre-boot plugged SFP autoneg advertisement

[<markus.stockhausen@gmx.de>]

> Von: markus.stockhausen@gmx.de <markus.stockhausen@gmx.de> 
> Gesendet: Sonntag, 19. April 2026 10:49
> An: 'Andrew Lunn' <andrew@lunn.ch>
> Betreff: AW: pre-boot plugged SFP autoneg advertisement
>
> Took that hint/question and digged deeper. Added further debug
> to each and every linkmode_copy. I think I found the culprit in 
> a userspace ethtool call. For now I assume OpenWrt netifd.

Hi Andrew,

once again thanks for your help. After further investigation I hopefully can
add 
more details. I think I got the whole picture now. So some additional
background 
information about the environment. 

- Realtek RTL930x devices with SFP+ module slots
- These are driven directly by a SerDes (controlled by downstream PCS
driver)
- The DTS reads

	port11: port@11 { 
		reg = <11>;
		label = "lan12" ;
		pcs-handle = <&serdes8>;
		phy-mode = "1000base-x";
		sfp = <&sfp1>;
		managed = "in-band-status";
	};

Sequence of events during boot is as follows:

- SFP module is already inserted (in my case 1G)
- phylink_sfp_config_phy() runs long before any network config starts
- OpenWrt netifd daemon starts and wants to configure the network interfaces
- It reads current settings via ethtool ioctl and gets autoneg=off
- It writes basic config values via ethtool ioctl including autneg=off
- Later on it starts the interface and phylink_start() is issued

With my limited knowledge I would patch phylink_ethtool_ksettings_get().

		/* The MAC is reporting the link results from its own PCS
		 * layer via in-band status. Report these as the current
		 * link settings.
		 */
		phylink_get_ksettings(&link_state, kset);
		break;

+	case MLO_AN_PHY:
+		/* SFP module present at boot but phylink not yet started.
+		 * Return autonegotiation as set by
phylink_sfp_config_phy().
+		 */
+		if (pl->sfp_bus && !pl->phydev)
+			kset->base.autoneg =
+
linkmode_test_bit(ETHTOOL_LINK_MODE_Autoneg_BIT,
+
pl->link_config.advertising)
+				? AUTONEG_ENABLE : AUTONEG_DISABLE;
+		break;
	}

	return 0;
}

This comes from the observation that

- pl->link_config.advertising is filled by phylink_sfp_set_config()
- state MLO_AN_PHY is reported before phylink_start()
- state MLO_AN_INBAND is reported after phylink_start()

Is this reasonable or am I totally off?

Markus