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: <e01451e1-78c8-4cd1-90a4-0f9ea38b1ab2@rock-chips.com>
Date: Thu, 22 Jan 2026 09:44:10 +0800
From: Chaoyi Chen <chaoyi.chen@...k-chips.com>
To: Andrew Lunn <andrew@...n.ch>, 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>,
 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

Hi Andrew,

On 1/21/2026 8:57 PM, Andrew Lunn wrote:
> 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.
> 

These are measured values obtained from hardware signal testing.
They are not documented in the TRM.

-- 
Best, 
Chaoyi