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

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Message-ID: <44988e1e-3ccb-4840-aa39-f28331d3c340@lunn.ch>
Date: Tue, 27 May 2025 17:12:17 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: George Moussalem <george.moussalem@...look.com>,
	Krzysztof Kozlowski <krzk@...nel.org>,
	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

> does this sound like a generic enough problem to contemplate something
> common, or should we go with something like qcom,dac-preset-short-cable

I've seen a few other boards with back to back PHYs like this, and
they did not need any properties.

It could be this PHY does not conform to the standard, does not have
the needed dynamic range, and is getting saturated.

What we do have is:

  tx-amplitude-100base-tx-percent:
    description:
      Transmit amplitude gain applied for 100BASE-TX. 100% matches 2V
      peak-to-peak specified in ANSI X3.263. When omitted, the PHYs default
      will be left as is.

This is intended for actually boosting the amplitude, to deal with
losses between the PHY and the RJ-45 connector. So this is the
opposite.

The description of what the magic value does on this PHY suggests it
does more, and it cannot be represented as a percent. So i think a
vendor property is O.K.

   Andrew