linux-kernel - Re: [PATCH v2] arm64: dts: ti: k3-am62d2-evm: Fix missing RX delay for DP83867 PHY

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Message-ID: <32265181-6a16-4cb3-9cc8-52d4265c6646@lunn.ch>
Date: Wed, 21 Jan 2026 14:22:04 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Siddharth Vadapalli <s-vadapalli@...com>
Cc: nm@...com, vigneshr@...com, kristo@...nel.org, robh@...nel.org,
	krzk+dt@...nel.org, conor+dt@...nel.org, bb@...com, afd@...com,
	p-bhagat@...com, gehariprasath@...com, stable@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, srk@...com
Subject: Re: [PATCH v2] arm64: dts: ti: k3-am62d2-evm: Fix missing RX delay
 for DP83867 PHY

On Wed, Jan 21, 2026 at 11:15:50AM +0530, Siddharth Vadapalli wrote:
> MAC Ports 1 and 2 of the CPSW3G Ethernet Switch in the AM62D2 SoC are both
> connected to different instances of the DP83867 Ethernet PHY on the AM62D2
> EVM, with the 'phy-mode' set to 'rgmii-id'. The DP83867 Ethernet PHY has to
> add a 2 nanosecond delay on receive (from wire) based on the EVM design.
> 
> Since the device driver for the DP83867 Ethernet PHY coincidentally assumes
> that a 2 nanosecond receive delay has to be added in the absence of the
> 'ti,rx-internal-delay' property, Ethernet is functional.
> 
> However, since the device-tree is intended to describe the Hardware, and,
> the device driver for the DP83867 Ethernet PHY may change in the future,
> add the 'ti,rx-internal-delay' property and assign it the value
> 'DP83867_RGMIIDCTL_2_00_NS' which corresponds to a 2 nanosecond
> delay.

The driver will not change. Doing so will break boards, causing
regressions. Also, passing PHY_INTERFACE_MODE_RGMII_ID to the PHY
means the PHY should add 2ns, or the closet it can achieve. The PHY
driver does not coincidentally assumes that a 2 nanosecond receive
delay is required, it is required a 2ns delay is added.

So this patch is pointless.

Please drop it.

       Andrew