linux-kernel - Re: [PATCH 0/2] net: stmmac: allow sharing MDIO lines

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Message-ID: <54421791-75fa-4ed3-8432-e21184556cde@lunn.ch>
Date:   Mon, 7 Aug 2023 21:50:53 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Andrew Halaney <ahalaney@...hat.com>,
        Alex Elder <elder@...aro.org>,
        Srini Kandagatla <srinivas.kandagatla@...aro.org>,
        netdev@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH 0/2] net: stmmac: allow sharing MDIO lines

On Mon, Aug 07, 2023 at 09:31:00PM +0200, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> 
> Two MACs may share MDIO lines to the PHYs. Let's allow that in the
> stmmac driver by providing a new device-tree property allowing one MAC
> node to reference the MDIO bus defined on a second MAC node.

I don't understand why this is needed. phy-handle can point to a phy
on any MDIO bus. So it is no problem for one MAC to point to the other
MACs MDIO bus as is.

You do sometimes get into ordering problems, especially if MAC0 is
pointing to a PHY on MAC1 MDIO bus. But MAC0 should get a
-EPROBE_DEFER, MAC1 then probes, creating its MDIO bus and the two
PHYs on it, and then later MAC0 is probes again and is successful.

     Andrew