netdev - Re: DT options for DSA user port with internal PHY

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Message-ID: <8eb8885f-2307-4ad4-9302-8423ba4db67d@lunn.ch>
Date: Tue, 4 Feb 2025 14:13:14 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Frieder Schrempf <frieder.schrempf@...tron.de>
Cc: "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: DT options for DSA user port with internal PHY

On Tue, Feb 04, 2025 at 09:30:23AM +0100, Frieder Schrempf wrote:
> Hi,
> 
> I'm using a KSZ9477 and I'm configuring the DSA user ports in the
> devicetree.
> 
> Due to the hardware implementation I need to use some options that
> currently seem to be unsupported by the driver.
> 
> First the user ports are physically limited to a maximum speed of
> 100MBit/s. As the MAC and the PHYs are capable of 1G, this also what
> gets advertised during autoneg.
> 
> Second the LEDs controlled by the PHY need to be handled in "Single
> Mode" instead of "Dual Mode".
> 
> Usually on an external PHY that gets probed separately, I could use
> "max-speed" and "micrel,led-mode" to achieve this.
> 
> But for the KSZ9477 the PHYs are not probed but instead hooked into the
> switch driver and from the PHY driver I don't seem to have any way to
> access the DT node for the DSA user port.
> 
> What would be the proper way to implement this? Any ideas?

The normal way to do this is add an mdio node, and use phy-handle in
the ports to point to the PHY on the MDIO bus. The PHY are then probed
in the usual ways, and you can have DT properties.

	Andrew