[PATCH v3 8/8] dt-bindings: net: ethernet-controller: tabulate who adds the RGMII delays

[Conor Dooley]

On Sat, Oct 10, 2026 at 11:59:00AM +0100, Lucas Tanure wrote:
> The informative section explains in prose how phy-mode, the delay
> properties in the MAC node and the mode handed to the PHY fit together,
> and says itself that developers often get this wrong. A reader has to
> work through several paragraphs before answering the one question they
> usually have: for this phy-mode and these properties, which part adds
> which delay.
> 
> Add a table that answers it at a glance, with one row for every
> combination the properties allow.
> 
> Assisted-by: LLM
> Signed-off-by: Lucas Tanure <tanure at linux.com>

If the net guys think this is valuable,
Acked-by: Conor Dooley <conor.dooley at microchip.com>

(although for something like this, us acking probably ain't needed,
ehh?)

> ---
>  .../bindings/net/ethernet-controller.yaml      | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/net/ethernet-controller.yaml b/Documentation/devicetree/bindings/net/ethernet-controller.yaml
> index 1bafd687dcb1..bba27a9feb61 100644
> --- a/Documentation/devicetree/bindings/net/ethernet-controller.yaml
> +++ b/Documentation/devicetree/bindings/net/ethernet-controller.yaml
> @@ -339,6 +339,24 @@ additionalProperties: true
>  # has added. Failure to remove the delay will result in a
>  # non-functioning link.
>  #
> +# Put together, with the two properties in the MAC node, this is who
> +# adds each delay:
> +#
> +#   phy-mode    tx-internal-delay-ps  rx-internal-delay-ps  TX delay    RX delay
> +#   rgmii       -                     -                     PCB trace   PCB trace
> +#   rgmii-id    -                     -                     PHY         PHY
> +#   rgmii-id    present               -                     MAC         PHY
> +#   rgmii-id    -                     present               PHY         MAC
> +#   rgmii-id    present               present               MAC         MAC
> +#   rgmii-txid  -                     -                     PHY         PCB trace
> +#   rgmii-txid  present               -                     MAC         PCB trace
> +#   rgmii-rxid  -                     -                     PCB trace   PHY
> +#   rgmii-rxid  -                     present               PCB trace   MAC
> +#
> +# A property for a clock the PCB already delays is not in this table.
> +# It is either the fine tuning described next, or a mistake the MAC
> +# should report as a fatal error.
> +#
>  # Sometimes there is a need to fine tune the delays. Often the MAC or
>  # PHY can perform this fine tuning. In the MAC node, the Device Tree
>  # properties 'rx-internal-delay-ps' and 'tx-internal-delay-ps' should
> -- 
> 2.56.0
> 
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