linux-kernel - Re: [PATCH net-next v2 06/13] dt-bindings: net: dsa: lantiq,gswip: add support for MII delay properties

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Message-ID: <59511487-6aa2-4615-9eb3-79aa0e9954ee@bootlin.com>
Date: Sat, 25 Oct 2025 18:30:21 +0200
From: Maxime Chevallier <maxime.chevallier@...tlin.com>
To: Daniel Golle <daniel@...rotopia.org>, Hauke Mehrtens <hauke@...ke-m.de>,
 Andrew Lunn <andrew@...n.ch>, Vladimir Oltean <olteanv@...il.com>,
 "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>, Simon Horman <horms@...nel.org>,
 Russell King <linux@...linux.org.uk>, netdev@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: Andreas Schirm <andreas.schirm@...mens.com>,
 Lukas Stockmann <lukas.stockmann@...mens.com>,
 Alexander Sverdlin <alexander.sverdlin@...mens.com>,
 Peter Christen <peter.christen@...mens.com>,
 Avinash Jayaraman <ajayaraman@...linear.com>, Bing tao Xu
 <bxu@...linear.com>, Liang Xu <lxu@...linear.com>,
 Juraj Povazanec <jpovazanec@...linear.com>,
 "Fanni (Fang-Yi) Chan" <fchan@...linear.com>,
 "Benny (Ying-Tsan) Weng" <yweng@...linear.com>,
 "Livia M. Rosu" <lrosu@...linear.com>, John Crispin <john@...ozen.org>
Subject: Re: [PATCH net-next v2 06/13] dt-bindings: net: dsa: lantiq,gswip:
 add support for MII delay properties

Hi Daniel,

On 25/10/2025 16:49, Daniel Golle wrote:
> Add support for standard tx-internal-delay-ps and rx-internal-delay-ps
> properties on port nodes to allow fine-tuning of RGMII clock delays.
> 
> The GSWIP switch hardware supports delay values in 500 picosecond
> increments from 0 to 3500 picoseconds, with a default of 2000
> picoseconds for both TX and RX delays.
> 
> This corresponds to the driver changes that allow adjusting MII delays
> using Device Tree properties instead of relying solely on the PHY
> interface mode.
> 
> Signed-off-by: Daniel Golle <daniel@...rotopia.org>
> ---
>  .../bindings/net/dsa/lantiq,gswip.yaml        | 20 +++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/net/dsa/lantiq,gswip.yaml b/Documentation/devicetree/bindings/net/dsa/lantiq,gswip.yaml
> index f3154b19af78..ed274bfb8d49 100644
> --- a/Documentation/devicetree/bindings/net/dsa/lantiq,gswip.yaml
> +++ b/Documentation/devicetree/bindings/net/dsa/lantiq,gswip.yaml
> @@ -8,6 +8,24 @@ title: Lantiq GSWIP Ethernet switches
>  
>  allOf:
>    - $ref: dsa.yaml#/$defs/ethernet-ports
> +  - properties:
> +      ports:
> +        patternProperties:
> +          "^port@[0-6]$":
> +            type: object
> +            properties:
> +              tx-internal-delay-ps:
> +                enum: [0, 500, 1000, 1500, 2000, 2500, 3000, 3500]
> +                default: 2000
> +                description:
> +                  RGMII TX Clock Delay defined in pico seconds.
> +                  The delay lines adjust the MII clock vs. data timing.
> +              rx-internal-delay-ps:
> +                enum: [0, 500, 1000, 1500, 2000, 2500, 3000, 3500]
> +                default: 2000
> +                description:
> +                  RGMII RX Clock Delay defined in pico seconds.
> +                  The delay lines adjust the MII clock vs. data timing.
>  
>  maintainers:
>    - Hauke Mehrtens <hauke@...ke-m.de>
> @@ -115,6 +133,8 @@ examples:
>                              label = "lan3";
>                              phy-mode = "rgmii";
>                              phy-handle = <&phy0>;
> +                            tx-internal-delay-ps = <2000>;
> +                            rx-internal-delay-ps = <2000>;

I guess that in this example, with a 2ns delay, this is no longer
"rgmii" but "rgmii-id", as delays are inserted by the switch. It would
make sense to update the phy-mode.

>                      };
>  
>                      port@1 {

Maxime