linux-kernel - Re: [PATCH 4/4] arm64: dts: rockchip: Enable Ethernet controller on Radxa E20C

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Message-ID: <c7fe0371-76bc-4cb4-ade8-e22112c1475d@lunn.ch>
Date: Fri, 7 Mar 2025 14:25:58 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Jonas Karlman <jonas@...boo.se>
Cc: Heiko Stuebner <heiko@...ech.de>, Andrew Lunn <andrew+netdev@...n.ch>,
	"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>, Yao Zi <ziyao@...root.org>,
	linux-rockchip@...ts.infradead.org, netdev@...r.kernel.org,
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] arm64: dts: rockchip: Enable Ethernet controller on
 Radxa E20C

On Fri, Mar 07, 2025 at 10:16:08AM +0100, Jonas Karlman wrote:
> Hi Andrew,
> 
> On 2025-03-06 23:49, Andrew Lunn wrote:
> >> +&mdio1 {
> >> +	rgmii_phy: ethernet-phy@1 {
> >> +		compatible = "ethernet-phy-ieee802.3-c22";
> > 
> > The compatible is not needed. That is the default.
> 
> Interesting, however I rather be explicit to not cause any issue for
> U-Boot or any other user of the device trees beside Linux kernel.

O.K.  But any system using Linux .dts files should be happy with no
compatible, since that is how the majority are. Because PHYs have ID
registers, generally there is no need for a compatible. The only time
you do need a compatible is:

* The ID registers are wrong
* The ID registers cannot be read, chicken/egg problems the driver needs to solve
* The Clause 22 address space is not implemented and you need to indicate C45
  should be used to get the ID registers.

None of this is specific to Linux.

	Andrew