netdev - Re: [PATCH net v2] dt-bindings: net: ethernet-controller: Add informative text about RGMII delays

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Message-ID: <20250501-extrude-jot-aa8512a299ec@spud>
Date: Thu, 1 May 2025 15:28:18 +0100
From: Conor Dooley <conor@...nel.org>
To: Andrew Lunn <andrew@...n.ch>
Cc: Rob Herring <robh@...nel.org>, Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Chaoyi Chen <chaoyi.chen@...k-chips.com>,
	Matthias Schiffer <matthias.schiffer@...tq-group.com>,
	"Russell King (Oracle)" <linux@...linux.org.uk>,
	Heiner Kallweit <hkallweit1@...il.com>, netdev@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v2] dt-bindings: net: ethernet-controller: Add
 informative text about RGMII delays

On Wed, Apr 30, 2025 at 11:21:35AM -0500, Andrew Lunn wrote:
> Device Tree and Ethernet MAC driver writers often misunderstand RGMII
> delays. Rewrite the Normative section in terms of the PCB, is the PCB
> adding the 2ns delay. This meaning was previous implied by the
> definition, but often wrongly interpreted due to the ambiguous wording
> and looking at the definition from the wrong perspective. The new
> definition concentrates clearly on the hardware, and should be less
> ambiguous.
> 
> Add an Informative section to the end of the binding describing in
> detail what the four RGMII delays mean. This expands on just the PCB
> meaning, adding in the implications for the MAC and PHY.
> 
> Additionally, when the MAC or PHY needs to add a delay, which is
> software configuration, describe how Linux does this, in the hope of
> reducing errors. Make it clear other users of device tree binding may
> implement the software configuration in other ways while still
> conforming to the binding.
> 
> Fixes: 9d3de3c58347 ("dt-bindings: net: Add YAML schemas for the generic Ethernet options")
> Signed-off-by: Andrew Lunn <andrew@...n.ch>
> ---
> Changes in v2:
> Reword Normative section
> manor->manner
> add when using phylib/phylink
> request details in the commit message and .dts comments
> clarify PHY -internal-delay-ps values being depending on rgmii-X mode.
> Link to v1: https://lore.kernel.org/r/20250429-v6-15-rc3-net-rgmii-delays-v1-1-f52664945741@lunn.ch
> ---
>  .../bindings/net/ethernet-controller.yaml          | 97 ++++++++++++++++++++--
>  1 file changed, 90 insertions(+), 7 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/net/ethernet-controller.yaml b/Documentation/devicetree/bindings/net/ethernet-controller.yaml
> index 45819b2358002bc75e876eddb4b2ca18017c04bd..a2d4c626f659a57fc7dcd39301f322c28afed69d 100644
> --- a/Documentation/devicetree/bindings/net/ethernet-controller.yaml
> +++ b/Documentation/devicetree/bindings/net/ethernet-controller.yaml
> @@ -74,19 +74,17 @@ properties:
>        - rev-rmii
>        - moca
>  
> -      # RX and TX delays are added by the MAC when required
> +      # RX and TX delays are provided by the PCB. See below

I'm not sure that "provided" is the correct word to describe what's
meant here (implemented might be better), but it's perfectly
understandable as-is and I don't think worth respinning or splitting
hairs over...

Acked-by: Conor Dooley <conor.dooley@...rochip.com>

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