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: <87589c3a-4888-4774-8743-770dbebb290d@lunn.ch>
Date: Wed, 21 Jan 2026 14:02:01 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Chaoyi Chen <chaoyi.chen@...k-chips.com>
Cc: Sebastian Reichel <sebastian.reichel@...labora.com>,
	Chaoyi Chen <kernel@...kyi.com>, 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>,
	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

> > That allows using standard properties in DT instead of vendor
> > specific "rx_delay"/"tx_delay". This results in a much better board
> > description and shows how far boards derive from the the standard
> > 2ns (which can use rgmii-id without any extra delay specification).
> > 
> 
> Oh, your approach was also my initial thought.
> 
> I first asked whether it would be more appropriate to implement this
> in the PHY or in the GMAC, and Andrew told me it should preferably be 
> done in the PHY. But I'm not sure whether all PHYs support this
> operation.
> 
> Andrew, would it be possible to implement this in the GMAC for cases
> where the PHY does not support it? Thanks.

As i commented to one of the patches, the PHY will be adding 2ns by
default when 'rgmii-id' is used. If you read the RGMII standard, you
also see there is quite a wide tolerance for these delays. So unless
there is a badly designed PCB which needs something well away from
2ns, i don't think it is necessary.

     Andrew