netdev - Re: [PATCH net] net: dsa: qca8k: forbid management frames access to internal PHYs if another device is on the MDIO bus

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Message-ID: <fd5dcd78-8eb7-4b60-853b-4f3d318d2e6a@lunn.ch>
Date: Fri, 25 Apr 2025 18:53:21 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Marek Behún <kabel@...nel.org>
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>,
	"Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
	"Rob Herring (Arm)" <robh@...nel.org>,
	Javier Carrasco <javier.carrasco.cruz@...il.com>,
	Wojciech Drewek <wojciech.drewek@...el.com>,
	Matthias Schiffer <mschiffer@...verse-factory.net>,
	Christian Marangi <ansuelsmth@...il.com>,
	Marek Mojík <marek.mojik@....cz>
Subject: Re: [PATCH net] net: dsa: qca8k: forbid management frames access to
 internal PHYs if another device is on the MDIO bus

> >From the ASCII art in commit 526c8ee04bdbd4d8 you can clearly see that
> I just assumed there is just one MDIO bus, because I saw activity on
> an oscilloscope. I didn't test it the way you now suggested. I also
> didn't think of the consequences for the driver design and
> device-trees. If we prove that there is just one MDIO bus with two
> masters instead of two separate buses that leak some noise in some
> situations, the situation will become more complicated...

It is not really that more complex. Some of the mv88e6xxx devices have
a similar architecture.

You need to throw away MDIO over Ethernet and stop using the switches
master. Because it is async, it cannot be used. The switch MDIO bus
driver then just issues bus transactions on the host MDIO bus, using
mdiobus_read_nested().

	Andrew