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

From: Lucas Tanure <tanure@linux.com>
To: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Cc: xianwei.zhao@amlogic.com, Andrew Lunn <andrew+netdev@lunn.ch>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@kernel.org>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Rob Herring <robh@kernel.org>,
	Krzysztof Kozlowski <krzk+dt@kernel.org>,
	Conor Dooley <conor+dt@kernel.org>,
	Neil Armstrong <neil.armstrong@linaro.org>,
	Kevin Hilman <khilman@baylibre.com>,
	Jerome Brunet <jbrunet@baylibre.com>,
	Maxime Chevallier <maxime.chevallier@bootlin.com>,
	Maxime Coquelin <mcoquelin.stm32@gmail.com>,
	Alexandre Torgue <alexandre.torgue@foss.st.com>,
	netdev@vger.kernel.org, devicetree@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-amlogic@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 8/8] dt-bindings: net: ethernet-controller: tabulate who adds the RGMII delays
Date: Thu, 22 Oct 2026 18:48:43 +0100	[thread overview]
Message-ID: <9b5fe9c2-aca1-4460-81fa-826e05e88c1a@linux.com> (raw)
In-Reply-To: <CAFBinCB8203vL6YK3+V2zDhz=qqeAwJoufPM60cD0Vz3s-OS6g@mail.gmail.com>

On 10/10/2026 23:37, Martin Blumenstingl wrote:
> Hi Andrew, Hi Lucas,
> 
> On Sat, Oct 10, 2026 at 12:59 PM Lucas Tanure <tanure@linux.com> wrote:
> [...]
>> +#   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
> We have some boards where the PCB traces result in part (1200ps) of
> the delay needed for RGMII (2000ps).
> The remainder (800ps) has to be added by either PHY or MAC: the
> (RTL8211F) PHY can only generate 0 or 2000ps delay so the MAC has to
> take over.
> For the three boards I have in mind, please see $ git grep
> rx-internal-delay-ps arch/arm64/boot/dts/amlogic/
> 
>> +# A property for a clock the PCB already delays is not in this table.
> Can you please explain this sentence (I'm not a native English speaker)?
> How I interpret the sentence: The PCB may add delays but those are
> implicit and not part of the {rx,tx}-internal-delay-ps properties. If
> the delays added by the PCB don't cover the full 2ns requirement then
> either MAC or PHY need to add the remainder, see fine-tuning below.
> 
>> +# It is either the fine tuning described next, or a mistake the MAC
>> +# should report as a fatal error.
> How can I differentiate between "fine tuning" and "mistake"?
> 
> 
> Best regards,
> Martin
The patch is wrong. It assumes a present property moves the 2ns from
the PHY to the MAC, and Andrew's reply on patch 4 says it does not.
I am dropping it in v4.

thanks
Lucas


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