linux-kernel - Re: [PATCH net-next v3 1/7] net: ethtool: pse-pd: Expand C33 PSE status with class, power and extended state

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Date: Tue, 25 Jun 2024 13:59:18 +0200
From: Kory Maincent <kory.maincent@...tlin.com>
To: Oleksij Rempel <o.rempel@...gutronix.de>
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
 <pabeni@...hat.com>, Donald Hunter <donald.hunter@...il.com>, Thomas
 Petazzoni <thomas.petazzoni@...tlin.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, Dent Project
 <dentproject@...uxfoundation.org>, kernel@...gutronix.de,
 UNGLinuxDriver@...rochip.com
Subject: Re: [PATCH net-next v3 1/7] net: ethtool: pse-pd: Expand C33 PSE
 status with class, power and extended state

On Tue, 25 Jun 2024 12:33:50 +0200
Oleksij Rempel <o.rempel@...gutronix.de> wrote:

> Hi Köry,
> 
> On Tue, Jun 25, 2024 at 11:18:35AM +0200, Kory Maincent wrote:
>  [...]  
>  [...]  
>  [...]  
>  [...]  
>  [...]  
> > 
> > In fact I can't test it, I have a splitter and an adjustable load, not a
> > splitter that can adjust it's own load. So I can't decrease the load of the
> > splitter itself and reach this error condition.  
> 
> Hm.. how about this setup:
> ------>>-----x--------->>----  
> PSE          |-load      splitter
> ------>>-----x--------->>----  
> 
> Attach the load directly to the ethernet line after PSE did
> classification with splitter. Then remove splitter. As long as load is
> high enough, PSE will not turn the port off. Then reduce load until it drops
> below the threshold.

That was a good idea but I can't managed do test it.
This is what I try: 
                       /---ethernet cable---PD
PSE===passive splitter=+
                       \---barrel cable---load

The active PD is well powered with PoE negotiation but there is no voltage at
the barrel cable of the passive splitter so the load is useless. :/ Maybe
passive splitter works only with passive injector.

Regards,
-- 
Köry Maincent, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com