linux-kernel - Re: [PATCH net-next v4 1/3] dt-bindings: net: ethernet-phy: add property tx-amplitude-100base-tx-percent

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Message-ID: <20250212192228.GA4383@debian>
Date: Wed, 12 Feb 2025 20:22:28 +0100
From: Dimitri Fedrau <dima.fedrau@...il.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: dimitri.fedrau@...bherr.com, Andrew Lunn <andrew+netdev@...n.ch>,
	"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>, Andrew Davis <afd@...com>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	Florian Fainelli <f.fainelli@...il.com>, netdev@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v4 1/3] dt-bindings: net: ethernet-phy: add
 property tx-amplitude-100base-tx-percent

Am Wed, Feb 12, 2025 at 02:04:02PM +0100 schrieb Andrew Lunn:
> On Tue, Feb 11, 2025 at 09:33:47AM +0100, Dimitri Fedrau via B4 Relay wrote:
> > From: Dimitri Fedrau <dimitri.fedrau@...bherr.com>
> > 
> > Add property tx-amplitude-100base-tx-percent in the device tree bindings
> > for configuring the tx amplitude of 100BASE-TX PHYs. Modifying it can be
> > necessary to compensate losses on the PCB and connector, so the voltages
> > measured on the RJ45 pins are conforming.
> > 
> > Signed-off-by: Dimitri Fedrau <dimitri.fedrau@...bherr.com>
> > ---
> >  Documentation/devicetree/bindings/net/ethernet-phy.yaml | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/net/ethernet-phy.yaml b/Documentation/devicetree/bindings/net/ethernet-phy.yaml
> > index 2c71454ae8e362e7032e44712949e12da6826070..e0c001f1690c1eb9b0386438f2d5558fd8c94eca 100644
> > --- a/Documentation/devicetree/bindings/net/ethernet-phy.yaml
> > +++ b/Documentation/devicetree/bindings/net/ethernet-phy.yaml
> > @@ -232,6 +232,12 @@ properties:
> >        PHY's that have configurable TX internal delays. If this property is
> >        present then the PHY applies the TX delay.
> >  
> > +  tx-amplitude-100base-tx-percent:
> > +    description:
> > +      Transmit amplitude gain applied for 100BASE-TX. When omitted, the PHYs
> > +      default will be left as is.
> > +    default: 100
> 
> Doesn't having a default statement contradict the text? Maybe the
> bootloader has set it to 110%, the text suggests it will be left at
> that, but the default value of 100 means it will get set back to 100%?
>
You are right, will remove the default statement.

> What do your driver changes actually do?

Only if tx-amplitude-100base-tx-percent is present, the amplitude should
be changed.

Best regards,
Dimitri Fedrau