netdev - Re: Aquantia PHY in OCSGMII mode?

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Message-ID: <aK68-Bp77-HiOAJk@shell.armlinux.org.uk>
Date: Wed, 27 Aug 2025 09:08:24 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Alexander Wilhelm <alexander.wilhelm@...termo.com>
Cc: Vladimir Oltean <vladimir.oltean@....com>, 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, Aug 27, 2025 at 07:57:28AM +0200, Alexander Wilhelm wrote:
> Hi Vladimir,
> 
> One of our hardware engineers has looked into the issue with the 100M link and
> found the following: the Aquantia AQR115 always uses 2500BASE-X (GMII) on the
> host side. For both 1G and 100M operation, it enables pause rate adaptation.
> However, our MAC only applies rate adaptation for 1G links. For 100M, it uses a
> 10x symbol replication instead.

This sounds like a misunderstanding, specifically:

"our MAC only applies rate adaptation for 1G links. For 100M, it uses
10x symbol replication instead."

It is the PHY that does rate adaption, so the MAC doesn't need to
support other speeds. Therefore, if the PHY is using a 2.5Gbps link
to the MAC with rate adaption for 100M, then the MAC needs to operate
at that 2.5Gbps speed.

You don't program the MAC differently depending on the media side
speed, unlike when rate adaption is not being used.

-- 
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