netdev - Re: [PATCH net-next] net: dsa: honor "max-speed" for implicit PHYs on user ports

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Message-ID: <20241219174626.6ga354quln36v4de@skbuf>
Date: Thu, 19 Dec 2024 19:46:26 +0200
From: Vladimir Oltean <olteanv@...il.com>
To: "A. Sverdlin" <alexander.sverdlin@...mens.com>
Cc: netdev@...r.kernel.org, Andrew Lunn <andrew@...n.ch>
Subject: Re: [PATCH net-next] net: dsa: honor "max-speed" for implicit PHYs
 on user ports

On Thu, Dec 19, 2024 at 06:38:01PM +0100, A. Sverdlin wrote:
> From: Alexander Sverdlin <alexander.sverdlin@...mens.com>
> 
> If the PHYs on user ports are not specified explicitly, but a common
> user_mii_bus is being registered and scanned there is no way to limit
> Auto Negotiation options currently. If a gigabit switch is deployed in a
> way that the ports cannot support gigabit rates (4-wire PCB/magnetics,
> for instance), there is no way to limit ports' AN not to advertise gigabit
> options. Some PHYs take considerably longer time to AutoNegotiate in such
> cases.
> 
> Provide a way to limit AN advertisement options by examining "max-speed"
> property in the DT node of the corresponding user port and call
> phy_set_max_speed() right before attaching the PHY to he port netdevice.
> 
> Signed-off-by: Alexander Sverdlin <alexander.sverdlin@...mens.com>
> ---

The user_mii_bus mechanism is redundant when we have device tree
available (as opposed to probing on platform data), let's not make it
even more redundant. Why don't you just declare the MDIO bus in the
device tree, with the PHYs on it, and place max-speed there?