linux-kernel - Re: [PATCH 1/5] dt-bindings: net: qca,ar803x: Add IPQ5018 Internal GE PHY support

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Message-ID: <1a6caebd-251f-4929-a7cf-af7c38ca30ed@lunn.ch>
Date: Mon, 26 May 2025 15:34:02 +0200
From: Andrew Lunn <andrew@...n.ch>
To: George Moussalem <george.moussalem@...look.com>
Cc: Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <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>,
	Florian Fainelli <f.fainelli@...il.com>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konradybcio@...nel.org>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...nel.org>, netdev@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, linux-clk@...r.kernel.org
Subject: Re: [PATCH 1/5] dt-bindings: net: qca,ar803x: Add IPQ5018 Internal
 GE PHY support

> I couldn't agree more but I just don't know what these values are exactly as
> they aren't documented anywhere. I'm working off the downstream QCA-SSDK
> codelinaro repo. My *best guess* for the MDAC value is that it halves the
> amplitude and current for short cable length, but I don't know what
> algorithm is used for error detection and correction.
> 
> What I do know is that values must be written in a phy to phy link
> architecture as the 'cable length' is short, a few cm at most. Without
> setting these values, the link doesn't work.
> 
> With the lack of proper documentation, I could move the values to the driver
> itself and convert it to a boolean property such as qca,phy-to-phy-dac or
> something..

Making it a boolean property is good. Please include in the binding
the behaviour when the bool is not present.

What you are really describing here is a sort cable, not phy-to-phy,
since a PHY is always connected to another PHY. So i think the
property name should be about the sort cable/distance.

	Andrew