netdev - Re: [PATCH net-next v6 3/3] net: dsa: yt921x: Add support for Motorcomm YT921x

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Message-ID: <d87a35c8-3d4c-469b-a490-9be116b982f3@lunn.ch>
Date: Sun, 24 Aug 2025 21:14:21 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Yangfl <mmyangfl@...il.com>
Cc: netdev@...r.kernel.org, Vladimir Oltean <olteanv@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Simon Horman <horms@...nel.org>,
	Russell King <linux@...linux.org.uk>, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v6 3/3] net: dsa: yt921x: Add support for
 Motorcomm YT921x

> Port 10 is dedicated to the internal MCU. Although I could not use it,
> anyone familiar with the chips would know it's Port 10 that is neither
> internal nor external.

The mv88e639X family has an internal Z80 CPU and its own port on the
switch. You will see code like:

                .num_ports = 11,        /* 10 + Z80 */
                .num_internal_phys = 8,

It is considered external, in that there is no internal PHY attached
In theory you could list it in DT, to instantiate the port, and then i
guess bad things to happen :-(

The good thing about this is, if you actually try use both the Z80 and
DSA to manage the switch, bad things are going to happen anyway.

So i would say there is some flexibility here, given how other drivers
handle this.

	Andrew