linux-kernel - Re: [PATCH net-next v3 14/17] dt-bindings: net: pse-pd: Add bindings for PD692x0 PSE controller

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Date: Mon, 19 Feb 2024 17:07:43 +0100
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Köry Maincent <kory.maincent@...tlin.com>
Cc: Andrew Lunn <andrew@...n.ch>, Rob Herring <robh@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Jonathan Corbet <corbet@....net>,
	Luis Chamberlain <mcgrof@...nel.org>,
	Russ Weight <russ.weight@...ux.dev>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>, Mark Brown <broonie@...nel.org>,
	Frank Rowand <frowand.list@...il.com>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org, devicetree@...r.kernel.org,
	Dent Project <dentproject@...uxfoundation.org>
Subject: Re: [PATCH net-next v3 14/17] dt-bindings: net: pse-pd: Add bindings
 for PD692x0 PSE controller

On Mon, Feb 19, 2024 at 03:31:06PM +0100, Köry Maincent wrote:
> On Fri, 16 Feb 2024 08:47:14 +0100
> Oleksij Rempel <o.rempel@...gutronix.de> wrote:
> > >
> > > So, either somebody needs to understand 1000BaseT and can say the
> > > proposed binding works, or we explicitly document the binding is
> > > limited to 10BaseT and 100BaseT.  
> > 
> > I asked the internet and found the answer: Some PSE/PD implementations
> > are not compatible with 1000BaseT.
> > 
> > See Figure 33–4—10BASE-T/100BASE-TX Endpoint PSE location overview.
> > Alternative B show a variant where power is injected directly to pairs
> > without using magnetics as it is done for Alternative A (phantom
> > delivery - over magnetics).
> > 
> > So, we have following variants of 2 pairs PoE:
> > +---------+---------------+-------------------+---------------------+--------------------+
> > | Variant | Alternative   | Polarity          | Power Feeding Type  |
> > Compatibility with | |         | (a/b)         | (Direct/Reverse)  |
> > (Direct/Phantom)    | 1000BaseT          |
> > +=========+===============+===================+=====================+====================+
> > | 1       | a             | Direct            | Phantom             | Yes
> >            |
> > +---------+---------------+-------------------+---------------------+--------------------+
> > | 2       | a             | Reverse           | Phantom             | Yes
> >            |
> > +---------+---------------+-------------------+---------------------+--------------------+
> > | 3       | b             | Direct            | Phantom             | Yes
> >            |
> > +---------+---------------+-------------------+---------------------+--------------------+
> > | 4       | b             | Reverse           | Phantom             | Yes
> >            |
> > +---------+---------------+-------------------+---------------------+--------------------+
> > | 5       | b             | Direct            | Direct              | No
> >            |
> > +---------+---------------+-------------------+---------------------+--------------------+
> > | 6       | b             | Reverse           | Direct              | No
> >            |
> > +---------+---------------+-------------------+---------------------+--------------------+
> 
> Maybe we could remove the polarity column on this table as it does not bring
> more information. It is also already explained on the PI pinout alternatives
> table.

Ack. I'm still not sure if "Phantom" is correct description.

> 
> Also we should document that a 4pairs PSE supporting only 10/100BaseT (which
> mean no magnetics on pinout AlternativeB) may not be compatible with a 4pairs
> 1GBaseT PD.

Ack. s/may not/is not/ :) and 4pairs PSE is not always compatible with
PoE4 as well. I assume this  kind of knowledge we will get from PSE
driver.

Regards,
Oleksij

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