linux-kernel - Re: [PATCH] arm64: dts: rockchip: use MAC TX delay for ROCK 4D

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Message-ID: <f22243f5-759a-4ff2-8d14-6edb49d87c52@lunn.ch>
Date: Thu, 24 Jul 2025 17:51:16 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Sebastian Reichel <sebastian.reichel@...labora.com>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Heiko Stuebner <heiko@...ech.de>, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kernel@...labora.com
Subject: Re: [PATCH] arm64: dts: rockchip: use MAC TX delay for ROCK 4D

>  &gmac0 {
>  	clock_in_out = "output";
>  	phy-handle = <&rgmii_phy0>;
> -	phy-mode = "rgmii-id";
> +	phy-mode = "rgmii-rxid";
>  	pinctrl-names = "default";
>  	pinctrl-0 = <&eth0m0_miim
>  		     &eth0m0_tx_bus2
> @@ -246,6 +246,8 @@ &eth0m0_rgmii_clk
>  		     &eth0m0_rgmii_bus
>  		     &ethm0_clk0_25m_out>;
>  	status = "okay";
> +	tx_delay = <0x20>;
> +	rx_delay = <0x00>;

What does 0x20 mean? Is it less than 2ns, or greater than 2ns?

Have you tried "rgmii-id" and small values for tx_delay? If the
hardware needs 2.1ns, for example, the MAC could add 0.1ns and the PHY
adds the default 2ns. That would allow you to conform to the DT
binding.

What PHY is this? Have you looked it you can control the delays the
PHY adds? If you actually need a delay of 1.9ns, maybe the PHY can be
configured to do this? That would also allow you to conform to the DT
binding.

	Andrew