linux-kernel - Re: [PATCH net-next RFC 0/5] net: phy: Introduce a port representation

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Message-ID: <Z300BuATJoVDc_4S@pengutronix.de>
Date: Tue, 7 Jan 2025 15:02:46 +0100
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Kory Maincent <kory.maincent@...tlin.com>
Cc: "Russell King (Oracle)" <linux@...linux.org.uk>,
	Maxime Chevallier <maxime.chevallier@...tlin.com>,
	davem@...emloft.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, thomas.petazzoni@...tlin.com,
	Andrew Lunn <andrew@...n.ch>, Jakub Kicinski <kuba@...nel.org>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	linux-arm-kernel@...ts.infradead.org,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Herve Codina <herve.codina@...tlin.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Vladimir Oltean <vladimir.oltean@....com>,
	Marek Behún <kabel@...nel.org>,
	Nicolò Veronese <nicveronese@...il.com>,
	Simon Horman <horms@...nel.org>, mwojtas@...omium.org,
	Antoine Tenart <atenart@...nel.org>
Subject: Re: [PATCH net-next RFC 0/5] net: phy: Introduce a port
 representation

On Tue, Jan 07, 2025 at 02:26:05PM +0100, Kory Maincent wrote:
> On Thu, 2 Jan 2025 18:03:52 +0100
> Oleksij Rempel <o.rempel@...gutronix.de> wrote:
> 
> > On Thu, Jan 02, 2025 at 10:48:05AM +0000, Russell King (Oracle) wrote:
> > > On Sun, Dec 22, 2024 at 07:54:37PM +0100, Oleksij Rempel wrote:  
> > > > Here is updated version:
> > > > 
> > > > ports {
> > > >     /* 1000BaseT Port with Ethernet and simple PoE */
> > > >     port0: ethernet-port@0 {
> > > >         reg = <0>; /* Port index */
> > > >         label = "ETH0"; /* Physical label on the device */
> > > >         connector = "RJ45"; /* Connector type */
> > > >         supported-modes = <10BaseT 100BaseTX 1000BaseT>; /* Supported
> > > > modes */
> > > > 
> > > >         transformer {
> > > >             model = "ABC123"; /* Transformer model number */
> > > >             manufacturer = "TransformerCo"; /* Manufacturer name */
> > > > 
> > > >             pairs {
> > > >                 pair@0 {
> > > >                     name = "A"; /* Pair A */
> > > >                     pins = <1 2>; /* Connector pins */
> > > >                     phy-mapping = <PHY_TX0_P PHY_TX0_N>; /* PHY pin
> > > > mapping */ center-tap = "CT0"; /* Central tap identifier */
> > > >                     pse-negative = <PSE_GND>; /* CT0 connected to GND */
> > > >                 };
> > > >                 pair@1 {
> > > >                     name = "B"; /* Pair B */
> > > >                     pins = <3 6>; /* Connector pins */
> > > >                     phy-mapping = <PHY_RX0_P PHY_RX0_N>;
> > > >                     center-tap = "CT1"; /* Central tap identifier */
> > > >                     pse-positive = <PSE_OUT0>; /* CT1 connected to
> > > > PSE_OUT0 */ };
> > > >                 pair@2 {
> > > >                     name = "C"; /* Pair C */
> > > >                     pins = <4 5>; /* Connector pins */
> > > >                     phy-mapping = <PHY_TXRX1_P PHY_TXRX1_N>; /* PHY
> > > > connection only */ center-tap = "CT2"; /* Central tap identifier */
> > > >                     /* No power connection to CT2 */
> > > >                 };
> > > >                 pair@3 {
> > > >                     name = "D"; /* Pair D */
> > > >                     pins = <7 8>; /* Connector pins */
> > > >                     phy-mapping = <PHY_TXRX2_P PHY_TXRX2_N>; /* PHY
> > > > connection only */ center-tap = "CT3"; /* Central tap identifier */
> > > >                     /* No power connection to CT3 */
> > > >                 };
> > > >             };
> > > >         };  
> 
> Couldn't we begin with something simple like the following and add all the
> transformers and pairs information as you described later if the community feels
> we need it?
> 
> mdis {
> 
>     /* 1000BaseT Port with Ethernet and PoE */
>     mdi0: ethernet-mdi@0 {
>         reg = <0>; /* Port index */
>         label = "ETH0"; /* Physical label on the device */
>         connector = "RJ45"; /* Connector type */
>         supported-modes = <10BaseT 100BaseTX 1000BaseT>; /* Supported modes */
>         lanes = <2>;
>         variant = "MDI-X"; /* MDI or MDI-X */
>         pse = <&pse1>;
>     };
> };

The problematic properties are lanes and variants.

Lanes seems to not provide any additional information which is not
provided by the supported-modes.

We have at least following working variants, which are supported by (some?)
microchip PHYs:
https://microchip.my.site.com/s/article/1000Base-T-Differential-Pair-Swapping
For swapping A and B pairs, we may use MDI/MDI-X. What is about swapped
C and D pairs?

The IEEE 802.3 - 2022 has following variants:
14.5.2 Crossover function - only A<>B swap is supported
40.4.4 Automatic MDI/MDI-X Configuration - only A<>B swap is supported?
55.4.4 Automatic MDI/MDI-X configuration - 4 swap variants are supported
113.4.4 Automatic MDI/MDI-X configuration - 4 swap variants are supported
126.4.4 Automatic MDI/MDI-X configuration - 4 swap variants are supported

This was only the pair swap. How to reflect the polarity swap withing
the pairs?

> We can also add led, thermal and fuse subnodes later.
> Let's begin with something simple for the initial support, considering
> that it has places for additional details in the future.

Yes :)

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