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

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Message-ID: <5a15d8eb-d6e9-46cf-9b33-d0a04e01b365@leica-geosystems.com>
Date: Fri, 9 Feb 2024 15:07:01 +0000
From: POPESCU Catalin <catalin.popescu@...ca-geosystems.com>
To: Andrew Lunn <andrew@...n.ch>
CC: "davem@...emloft.net" <davem@...emloft.net>, "kuba@...nel.org"
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Subject: Re: [PATCH v3 2/2] net: phy: dp83826: support TX data voltage tuning

On 09.02.24 15:07, Andrew Lunn wrote:
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> 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.

Indeed, the voltage drop (or loss) happens b/w the PHY and the connector 
(could be RJ45, LEMO, etc).
Trying to reformulate :

DP83826 offers the possibility to tune the voltage of logical levels of 
the MLT-3 encoded TX data. This is useful when there is a voltage drop 
in between the PHY and the connector and we want to increase the voltage 
levels to compensate for that drop.

Is this more meaningful ?

>
>        Andrew