linux-kernel - Re: [PATCH 0/3] arm64: dts: rockchip: Change gmac phy-mode to rgmii-id for rk3576 board

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Message-ID: <b25d6eb2-e105-4060-86fa-c1a06396ca92@lunn.ch>
Date: Wed, 21 Jan 2026 13:57:19 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Chaoyi Chen <kernel@...kyi.com>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Heiko Stuebner <heiko@...ech.de>,
	Alexey Charkov <alchark@...il.com>,
	Shawn Lin <shawn.lin@...k-chips.com>,
	Sebastian Reichel <sebastian.reichel@...labora.com>,
	Chaoyi Chen <chaoyi.chen@...k-chips.com>,
	Andy Yan <andy.yan@...k-chips.com>,
	Nicolas Frattaroli <nicolas.frattaroli@...labora.com>,
	Detlev Casanova <detlev.casanova@...labora.com>,
	Stephen Chen <stephen@...xa.com>, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] arm64: dts: rockchip: Change gmac phy-mode to
 rgmii-id for rk3576 board

On Wed, Jan 21, 2026 at 11:15:45AM +0800, Chaoyi Chen wrote:
> From: Chaoyi Chen <chaoyi.chen@...k-chips.com>
> 
> According to the description in the net documentation, PHY modes
> "rgmii", "rgmii-rxid" and "rgmii-txid" modes require the clock signal
> to be delayed on the PCB.
> 
> The Rockchip platform has long used the above mentioned PHY modes and
> private delay prop to describe the internal IO delay settings of the
> chip, which is inconsistent with what is described in the documentation.
> 
> Some background, for RK3576, you can assume that:
> 
>         tx_delay_time(ns) = 0.0579 * delay_line_count + 0.105

Where did this formula come from? Is it in the datasheet.

      Andrew