netdev - Re: [PATCH v3 2/2] net: phy: dp83826: support TX data voltage tuning

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Message-ID: <00691961-d516-4338-b7e8-203625e561ee@lunn.ch>
Date: Fri, 9 Feb 2024 15:07:20 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Catalin Popescu <catalin.popescu@...ca-geosystems.com>
Cc: davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
	robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
	conor+dt@...nel.org, afd@...com, hkallweit1@...il.com,
	linux@...linux.org.uk, netdev@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	bsp-development.geo@...ca-geosystems.com, m.felsch@...gutronix.de
Subject: Re: [PATCH v3 2/2] net: phy: dp83826: support TX data voltage tuning

On Fri, Feb 09, 2024 at 01:36:28PM +0100, Catalin Popescu wrote:
> DP83826 offers the possibility to tune the voltage of logical
> levels of the MLT-3 encoded TX data. This is especially interesting
> when the TX data path is lossy and we want to increase the voltage
> levels to compensate the loss.

Maybe i'm being nit-picky....

"TX data path is lossy" should probably be "TX data path as far as the
RJ46 socket is lossy". 802.3 probably defines the voltage at that
point. If you tune it so the voltage is too high at that point, you
are breaking the standard. So you can use this to adjust for losses in
your coupling and cable run to the front panel. You should not be
using this for range extension by cranking up the voltages. Yes, you
might be able to, but we should not be encouraging it.

      Andrew