linux-kernel - Re: [PATCH v2 4/4] arm: dts: stm32: Add Priva E-Measuringbox devicetree

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Message-ID: <eaec5732-7a24-46ba-8d76-7896304264ac@lunn.ch>
Date: Mon, 9 Dec 2024 17:44:14 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Oleksij Rempel <o.rempel@...gutronix.de>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Woojung Huh <woojung.huh@...rochip.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	Roan van Dijk <roan@...tonic.nl>, kernel@...gutronix.de,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	devicetree@...r.kernel.org,
	linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH v2 4/4] arm: dts: stm32: Add Priva E-Measuringbox
 devicetree

> +	/* DP83TD510E PHYs have max MDC rate of 1.75MHz.

Really? That breaks IEEE 802.3, which requires 2.5MHz. Humm, says it
multiple times in the datasheet. Seems like a language lawyer was
involved in the data sheet.

  The DP83TD510E is an ultra-low power Ethernet
  physical layer transceiver compliant with the IEEE
  802.3cg 10Base-T1L specification

I would not be surprised to find that 802.3cg says nothing about MDC,
that is in the base 802.3 standard, which they don't say they are
compliant to.

>        * Since we can't reduce
> +	 * stmmac MDC clock without reducing system bus rate, we need to use
> +	 * gpio based MDIO bus.
> +	 */

At least there is a simple workaround, even if it is much slower than
what you really need.

	Andrew