netdev - Re: [PATCH net] Revert "dsa: mv88e6xxx: make serdes SGMII/Fiber tx amplitude configurable"

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Message-ID: <ea3f1274-70bd-4b04-8f6e-468851e6fc8f@lunn.ch>
Date: Mon, 5 Jan 2026 15:24:18 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Vladimir Oltean <vladimir.oltean@....com>
Cc: netdev@...r.kernel.org, Russell King <linux@...linux.org.uk>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Marek Behún <kabel@...nel.org>,
	Holger Brunck <holger.brunck@...achienergy.com>
Subject: Re: [PATCH net] Revert "dsa: mv88e6xxx: make serdes SGMII/Fiber tx
 amplitude configurable"

On Sun, Jan 04, 2026 at 11:39:52AM +0200, Vladimir Oltean wrote:
> This reverts commit 926eae604403acfa27ba5b072af458e87e634a50, which
> never could have produced the intended effect:
> https://lore.kernel.org/netdev/AM0PR06MB10396BBF8B568D77556FC46F8F7DEA@AM0PR06MB10396.eurprd06.prod.outlook.com/
> 
> The reason why it is broken beyond repair in this form is that the
> mv88e6xxx driver outsources its "tx-p2p-microvolt" property to the OF
> node of an external Ethernet PHY. This:
> (a) does not work if there is no external PHY (chip-to-chip connection,
>     or SFP module)
> (b) pollutes the OF property namespace / bindings of said external PHY
>     ("tx-p2p-microvolt" could have meaning for the Ethernet PHY's SerDes
>     interface as well)
> 
> We can revisit the idea of making SerDes amplitude configurable once we
> have proper bindings for the mv88e6xxx SerDes. Until then, remove the
> code that leaves us with unnecessary baggage.
> 
> Fixes: 926eae604403 ("dsa: mv88e6xxx: make serdes SGMII/Fiber tx amplitude configurable")
> Cc: Holger Brunck <holger.brunck@...achienergy.com>
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>

Reviewed-by: Andrew Lunn <andrew@...n.ch>

    Andrew