netdev - Re: [PATCH net-next v2 00/10] define and enforce phylink bindings

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Message-ID: <ZQ2LMe9aa1ViBcSH@shell.armlinux.org.uk>
Date: Fri, 22 Sep 2023 13:40:17 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Arınç ÜNAL <arinc.unal@...nc9.com>,
	Rob Herring <robh+dt@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Conor Dooley <conor+dt@...nel.org>,
	George McCollister <george.mccollister@...il.com>,
	Andrew Lunn <andrew@...n.ch>,
	Florian Fainelli <f.fainelli@...il.com>,
	Vladimir Oltean <olteanv@...il.com>,
	Kurt Kanzenbach <kurt@...utronix.de>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Woojung Huh <woojung.huh@...rochip.com>,
	UNGLinuxDriver@...rochip.com,
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Subject: Re: [PATCH net-next v2 00/10] define and enforce phylink bindings

On Sat, Sep 16, 2023 at 02:08:52PM +0300, Arınç ÜNAL wrote:
> Hello there.
> 
> This patch series defines phylink bindings and enforces them for the
> ethernet controllers that need them.
> 
> Some schemas had to be changed to properly enforce phylink bindings for all
> of the affected ethernet controllers. Some of the documents of these
> ethernet controllers were non json-schema, which had to be converted.
> 
> I will convert the remaining documents to json-schema while this patch
> series receives reviews.

I can't say that I'm comfortable with this. We appear to be defining
bindings based on software implementation, and a desire for the DT
tooling to enforce what the software implementation wants. Isn't this
against the aims of device tree and device tree binding documentation?
Seems to me like feature-creep.

The bindings that phylink parses are already documented in the
ethernet controller yaml document. Specifically:

- phylink does not parse the phy-mode property, that is left to the
  implementation to pass to phylink, which can implement it any
  which way they choose (and even default to something.)

- phylink does not require a phy property - phylink does expect a PHY
  to be attached, but how that PHY is attached is up to the ethernet
  controller driver. It may call one of the phylink functions that
  parses the phy property, or it may manually supply the phy device to
  phylink. Either way, phylink does not itself require a PHY property.

- phylink does not require a sfp property - this obviously is optional.

So, all in all, ethernet-controller already describes it, and to create
a DT binding document that pretends that phylink requires any of this
stuff is, in my mind, wrong.

DSA requires certain properties by dint of the parsing and setup of
phylink being in generic code - this is not because phylink requires
certain properties, but phylink does require certain information in
order to function correctly.

The issue here is _how_ phylink gets that information, and as I state
above, it _can_ come from DT, but it can also be given that information
manually.

As an example, there are plenty of drivers in the tree which try to
parse a phy node, and if that's not present, they try to see if a PHY
exists at a default# bus address.

We seem to be digging outselves a hole here, where "phylink must have
these properties". No, that is wrong.

-- 
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