netdev - Re: Aquantia PHY in OCSGMII mode?

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Message-ID: <aOZm52L7k2bAEovF@FUE-ALEWI-WINX>
Date: Wed, 8 Oct 2025 15:28:07 +0200
From: Alexander Wilhelm <alexander.wilhelm@...termo.com>
To: Vladimir Oltean <vladimir.oltean@....com>
Cc: "Russell King (Oracle)" <linux@...linux.org.uk>,
        Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: Aquantia PHY in OCSGMII mode?

On Wed, Oct 08, 2025 at 02:10:59PM +0300, Vladimir Oltean wrote:
[...]
> For that, please break the link again, by making the following changes on top:
> 
> 1. Configure IF_MODE=3 (SGMII autoneg format) for 2500base-x:
> 
> diff --git a/drivers/net/pcs/pcs-lynx.c b/drivers/net/pcs/pcs-lynx.c
> index a88cbe67cc9d..ea42b8d813f3 100644
> --- a/drivers/net/pcs/pcs-lynx.c
> +++ b/drivers/net/pcs/pcs-lynx.c
> @@ -152,11 +152,10 @@ static int lynx_pcs_config_giga(struct mdio_device *pcs,
>  		mdiodev_write(pcs, LINK_TIMER_HI, link_timer >> 16);
>  	}
> 
> -	if (interface == PHY_INTERFACE_MODE_1000BASEX ||
> -	    interface == PHY_INTERFACE_MODE_2500BASEX) {
> +	if (interface == PHY_INTERFACE_MODE_1000BASEX) {
>  		if_mode = 0;
>  	} else {
> -		/* SGMII and QSGMII */
> +		/* SGMII, QSGMII and (incorrectly) 2500base-x */
>  		if_mode = IF_MODE_SGMII_EN;
>  		if (neg_mode == PHYLINK_PCS_NEG_INBAND_ENABLED)
>  			if_mode |= IF_MODE_USE_SGMII_AN;
> 
> 2. Edit your MAC OF node in the device tree and add:
> 
> &mac {
> 	managed = "in-band-status";  // this
> 	phy-mode = "2500base-x";
> };
> 
> This will reliably cause the same behaviour as before, but with no dependency on U-Boot.

I have the broken 100M link state again (IF_MODE=3). Below are the debug
details I was able to observe:

* With 2.5G link:

    mdio_bus 0x0000000ffe4e5000:00: BMSR 0x2d, BMCR 0x1140, ADV 0x41a0, LPA 0xdc01, IF_MODE 0x3

* With 1G link:

    mdio_bus 0x0000000ffe4e5000:00: BMSR 0x2d, BMCR 0x1140, ADV 0x41a0, LPA 0xd801, IF_MODE 0x3

* With 100M link:

    mdio_bus 0x0000000ffe4e5000:00: BMSR 0x2d, BMCR 0x1140, ADV 0x41a0, LPA 0xd401, IF_MODE 0x3

[...]
> Regarding my patch vs yours, my thoughts on this topic are: the bug is
> old, the PCS driver never worked if the registers were not as expected
> (this is not a regression), and your patch is incomplete if MII_BMCR
> also contains significant differences. I would recommend submitting
> mine, as a new feature to net-next, when it reopens for patches for 6.19.
> I've credited you with Co-developed-by due to the significance of your
> findings. Thanks.

Sure, thank you.


Best regards
Alexander Wilhelm