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

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Message-ID: <79ade357-0a6b-44e9-9a27-6722a11842f3@kontron.de>
Date: Tue, 25 Feb 2025 09:42:34 +0100
From: Frieder Schrempf <frieder.schrempf@...tron.de>
To: Andrew Lunn <andrew@...n.ch>
Cc: "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: DT options for DSA user port with internal PHY

On 04.02.25 2:13 PM, Andrew Lunn wrote:
> 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.

I see. That makes sense and it works just fine. Thanks!