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

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Message-ID: <8b166e41-8d21-4519-bd59-01b5ae877655@ti.com>
Date: Mon, 28 Apr 2025 19:58:42 +0530
From: Siddharth Vadapalli <s-vadapalli@...com>
To: Andrew Lunn <andrew@...n.ch>
CC: Matthias Schiffer <matthias.schiffer@...tq-group.com>,
        "Russell King
 (Oracle)" <linux@...linux.org.uk>,
        "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 Mon, Apr 28, 2025 at 04:08:10PM +0200, Andrew Lunn wrote:
> > > However, with the yaml stuff, if that is basically becoming "DT
> > > specification" then it needs to be clearly defined what each value
> > > actually means for the system, and not this vague airy-fairy thing
> > > we have now.
> 
>  
> > I agree with Russell that it seems preferable to make it unambiguous whether
> > delays are added on the MAC or PHY side, in particular for fine-tuning. If
> > anything is left to the implementation, we should make the range of acceptable
> > driver behavior very clear in the documentation.
> 
> I think we should try the "Informative" route first, see what the DT
> Maintainers think when we describe in detail how Linux interprets
> these values.
> 
> I don't think a whole new set of properties will solve anything. I
> would say the core of the problem is that there are multiple ways of
> getting a working system, many of which don't fit the DT binding. But
> DT developers don't care about that, they are just happy when it
> works. Adding a different set of properties won't change that.

Isn't the ambiguity arising due to an incomplete description wherein we
are not having an accurate description for the PCB Traces?

A complete description might be something like:

mac {
	pcb-traces {
		mac-to-phy-trace-delay = <X>; // Nanoseconds
		phy-to-mac-trace-delay = <Y>; // Nanoseconds
	};
	phy-mode = "rgmii-*";
	phy-handle = <&phy>;
};

In some designs, the "mac-to-phy-trace" and the "phy-to-mac-trace" are
treated as a part of the MAC block for example. Depending on which block
contains the trace, the delay is added accordingly.

Regards,
Siddharth.