netdev - Re: [PATCH net-next 1/4] dt-bindings: net: ethernet-controller: update descriptions of RGMII modes

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Message-ID: <94075f0a-6e17-4106-879e-3aa5193f9ef2@lunn.ch>
Date: Fri, 18 Apr 2025 22:26:55 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Matthias Schiffer <matthias.schiffer@...tq-group.com>
Cc: 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>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Andy Whitcroft <apw@...onical.com>,
	Dwaipayan Ray <dwaipayanray1@...il.com>,
	Lukas Bulwahn <lukas.bulwahn@...il.com>,
	Joe Perches <joe@...ches.com>, Jonathan Corbet <corbet@....net>,
	Nishanth Menon <nm@...com>, Vignesh Raghavendra <vigneshr@...com>,
	Siddharth Vadapalli <s-vadapalli@...com>,
	Roger Quadros <rogerq@...nel.org>, Tero Kristo <kristo@...nel.org>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux@...tq-group.com
Subject: Re: [PATCH net-next 1/4] dt-bindings: net: ethernet-controller:
 update descriptions of RGMII modes

On Tue, Apr 15, 2025 at 12:18:01PM +0200, Matthias Schiffer wrote:
> As discussed [1], the comments for the different rgmii(-*id) modes do not
> accurately describe what these values mean.
> 
> As the Device Tree is primarily supposed to describe the hardware and not
> its configuration, the different modes need to distinguish board designs
> (if a delay is built into the PCB using different trace lengths); whether
> a delay is added on the MAC or the PHY side when needed should not matter.
> 
> Unfortunately, implementation in MAC drivers is somewhat inconsistent
> where a delay is fixed or configurable on the MAC side. As a first step
> towards sorting this out, improve the documentation.
> 
> Link: https://lore.kernel.org/lkml/d25b1447-c28b-4998-b238-92672434dc28@lunn.ch/ [1]
> Signed-off-by: Matthias Schiffer <matthias.schiffer@...tq-group.com>
> ---
>  .../bindings/net/ethernet-controller.yaml        | 16 +++++++++-------
>  1 file changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/net/ethernet-controller.yaml b/Documentation/devicetree/bindings/net/ethernet-controller.yaml
> index 45819b2358002..2ddc1ce2439a6 100644
> --- a/Documentation/devicetree/bindings/net/ethernet-controller.yaml
> +++ b/Documentation/devicetree/bindings/net/ethernet-controller.yaml
> @@ -74,19 +74,21 @@ properties:
>        - rev-rmii
>        - moca
>  
> -      # RX and TX delays are added by the MAC when required
> +      # RX and TX delays are part of the board design (through PCB traces). MAC
> +      # and PHY must not add delays.
>        - rgmii
>  
> -      # RGMII with internal RX and TX delays provided by the PHY,
> -      # the MAC should not add the RX or TX delays in this case
> +      # RGMII with internal RX and TX delays provided by the MAC or PHY. No
> +      # delays are included in the board design; this is the most common case
> +      # in modern designs.
>        - rgmii-id
>  
> -      # RGMII with internal RX delay provided by the PHY, the MAC
> -      # should not add an RX delay in this case
> +      # RGMII with internal RX delay provided by the MAC or PHY. TX delay is
> +      # part of the board design.
>        - rgmii-rxid
>  
> -      # RGMII with internal TX delay provided by the PHY, the MAC
> -      # should not add an TX delay in this case
> +      # RGMII with internal TX delay provided by the MAC or PHY. RX delay is
> +      # part of the board design.

This looks good to me. There is nothing here which is Linux specific.

Reviewed-by: Andrew Lunn <andrew@...n.ch>

    Andrew