netdev - DT options for DSA user port with internal PHY

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Message-ID: <d1243bdc-3c88-4e15-b955-309d1917a599@kontron.de>
Date: Tue, 4 Feb 2025 09:30:23 +0100
From: Frieder Schrempf <frieder.schrempf@...tron.de>
To: "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: DT options for DSA user port with internal PHY

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?

Thanks
Frieder