linux-kernel - Re: [PATCH 2/2] net: phy: realtek: add dt property to disable broadcast PHY address

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Message-ID: <bc8c7c6a-5d5f-4f7c-a1e2-e10a6a82d50e@lunn.ch>
Date: Tue, 3 Dec 2024 01:04:51 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Zhiyuan Wan <kmlinuxm@...il.com>
Cc: kuba@...nel.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	willy.liu@...ltek.com, Yuki Lee <febrieac@...look.com>
Subject: Re: [PATCH 2/2] net: phy: realtek: add dt property to disable
 broadcast PHY address

On Tue, Dec 03, 2024 at 03:50:29AM +0800, Zhiyuan Wan wrote:
> This patch add support to disable 'broadcast PHY address' feature of
> RTL8211F.
> 
> This feature is enabled defaultly after a reset of this transceiver.
> When this feature is enabled, the phy not only responds to the
> configuration PHY address by pin states on board, but also responds
> to address 0, the optional broadcast address of the MDIO bus.
> 
> But not every transceiver supports this feature, when RTL8211
> shares one MDIO bus with other transceivers which doesn't support
> this feature, like mt7530 switch chip (integrated in mt7621 SoC),
> it usually causes address conflict, leads to the
> port of RTL8211FS stops working.

I think you can do this without needing a new property. The DT binding
has:

            reg = <4>;

This is the address the PHY should respond on. If reg is not 0, then
broadcast is not wanted.

If reg is 0, it means one of two things:

The DT author did not know about this broadcast feature, the PHY
appeared at address 0, so they wrote that. It might actually be
strapped to another address, but it does not matter.

The DT author wants it to use the broadcast address, it might even be
strapped to address 0.

Am i missing anything?

	Andrew