linux-kernel - Re: [PATCH v2] net: dsa: mv88e6xxx: fix external smi for mv88e6176

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Message-Id: <20250616191214.2295467-1-quantumcross@gmail.com>
Date: Mon, 16 Jun 2025 15:12:14 -0400
From: Robert Cross <quantumcross@...il.com>
To: andrew@...n.ch
Cc: bpf@...r.kernel.org,
	davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org,
	olteanv@...il.com,
	pabeni@...hat.com,
	quantumcross@...il.com
Subject: Re: [PATCH v2] net: dsa: mv88e6xxx: fix external smi for mv88e6176

> The MV88E6390_G2_SMI_PHY_CMD_FUNC_EXTERNAL bit is reserved on the 6352
> family.

Indeed it is...

> You are not understanding what i'm saying. This family has a single
> MDIO bus controller. That controller is used by both the internal PHY
> devices, plus there are two pins on the chip for external PHYs.
>
> All the PHYs will appear on that one MDIO bus controller.

So you're saying that if I removed my hack that apparently just sets
this reserved bit, and I take my PHY on port 6 and remove it from
the mdio_ext { compatible = "marvell,mv88e6xxx-mdio-external"; } entry
and put it in my mdio { } node it will direct requests to address 6 to
the external phy via the MDC/MDIO_PHY pins just fine?

I'm guessing it will just automatically enable or disable the external
SMI pins depending on the state of port 5 which shares pins?

I'm also guessing that ports 0, 1, 2, 3, and 4 will map to the
internal PHYs (because there are 5) and then ports 5 and 6
automagically externally...

I shudder to think how by what forbidden voodoo my current device
tree actually works with this hack...

Thank you so much for your explanation. Hopefully I'll have a
real substantive patch in the future :)