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

From: "Russell King (Oracle)" <[email-masked]>
Date: Tue, 7 Jan 2025 15:14:43 +0000

On Tue, Jan 07, 2025 at 03:02:46PM +0100, Oleksij Rempel wrote:
> On Tue, Jan 07, 2025 at 02:26:05PM +0100, Kory Maincent wrote:
> > On Thu, 2 Jan 2025 18:03:52 +0100
> > Oleksij Rempel <[email-masked]> 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?

802.3 supports this because of the problems caused by miswired cables,
which are typically a user thing. It's not really there to give freedom
to designers to wire their sockets incorrectly.

Do we have any real cases where a socket has been wired incorrectly?

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