linux-kernel - Re: [PATCH net-next 0/2] net: phy: dp83822: Add support for changing the transmit amplitude voltage

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Message-ID: <20250113141828.GA4250@debian>
Date: Mon, 13 Jan 2025 15:18:28 +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>, netdev@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 0/2] net: phy: dp83822: Add support for changing
 the transmit amplitude voltage

Hi Andrew,

Am Mon, Jan 13, 2025 at 02:54:28PM +0100 schrieb Andrew Lunn:
> On Mon, Jan 13, 2025 at 06:40:11AM +0100, Dimitri Fedrau via B4 Relay wrote:
> > Add support for changing the transmit amplitude voltage in 100BASE-TX mode.
> > Add support for configuration via DT.
> 
> The commit message is supposed to answer the question "Why?". Isn't
> reducing the voltage going to make the device non conforming? Why
> would i want to break it? I could understand setting it a bit higher
> than required to handle losses on the PCB and connector, so the
> voltages measured on the RJ45 pins are conforming.
>
- Will add the "Why?" to the commit description. You already answered it.
- Yes you are right.
- I don't want to break it, the PHY just provides these settings. And I
  just wanted to reflect this in the code, although it probably doesn't
  make sense.
- In my case I want to set it a bit higher to be conforming.

> Also, what makes the dp8382 special? I know other PHYs can actually do
> this. So why are we adding some vendor specific property just for
> 100base-tx?
>
I don't think that the dp83822 is special in this case. I just didn't
know better. Would be removing the vendor specific property enough ?
Or is there already a defined property describing this. Didn't found
anything.

Best regards,
Dimitri