RE: [EXT] Re: [PATCH net-next 3/9] net: phy: add kr phy connection type

[Florinel Iordache <florinel.iordache@nxp.com>]

> On Thu, Mar 26, 2020 at 03:51:16PM +0200, Florinel Iordache wrote:
> > Add support for backplane kr phy connection types currently available
> > (10gbase-kr, 40gbase-kr4) and the required phylink updates (cover all
> > the cases for KR modes which are clause 45 compatible to correctly
> > assign phy_interface and phylink#supported)
> >
> > Signed-off-by: Florinel Iordache <florinel.iordache@nxp.com>
> > ---
> >  drivers/net/phy/phylink.c | 15 ++++++++++++---
> >  include/linux/phy.h       |  6 +++++-
> >  2 files changed, 17 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
> > index fed0c59..db1bb87 100644
> > --- a/drivers/net/phy/phylink.c
> > +++ b/drivers/net/phy/phylink.c
> > @@ -4,6 +4,7 @@
> >   * technologies such as SFP cages where the PHY is hot-pluggable.
> >   *
> >   * Copyright (C) 2015 Russell King
> > + * Copyright 2020 NXP
> >   */
> >  #include <linux/ethtool.h>
> >  #include <linux/export.h>
> > @@ -303,7 +304,6 @@ static int phylink_parse_mode(struct phylink *pl, struct
> fwnode_handle *fwnode)
> >                       break;
> >
> >               case PHY_INTERFACE_MODE_USXGMII:
> > -             case PHY_INTERFACE_MODE_10GKR:
> 
> We might have a backwards compatibility issue here. If i remember correctly,
> there are some boards out in the wild using PHY_INTERFACE_MODE_10GKR not
> PHY_INTERFACE_MODE_10GBASER.
> 
> See e0f909bc3a242296da9ccff78277f26d4883a79d
> 
> Russell, what do you say about this?
> 
>          Andrew

Ethernet interface nomenclature is using the following terminology:
e.g. 10GBase-KR: data rate (10G),  modulation type (Base = Baseband),
medium type (K = BacKplane), physical layer encoding scheme
(R = scRambling/descRambling using 64b/66b encoding that allows for
Ethernet framing at a rate of 10.3125 Gbit/s)
So 10GBase-R name provide information only about the data rate and
the encoding scheme without specifying the interface medium.
10GBase-R is a family of many different standards specified for
several different physical medium for copper and optical fiber like
for example:
	10GBase-SR: Short range (over fiber)
	10GBase-LR: Long reach (over fiber)
	10GBase-LRM: Long reach multi-mode (over fiber)
	10GBase-ER: Extended reach (over fiber)
	10GBase-CR: 10G over copper
	10GBase-KR: Backplane

10GBase-KR represents Ethernet operation over electrical backplanes on
single lane and uses the same physical layer encoding as 10GBase-LR/ER/SR
defined in IEEE802.3 Clause 49. 
So prior to my change, phy_interface_t provided both enumerators which is correct:
	PHY_INTERFACE_MODE_10GBASER
	PHY_INTERFACE_MODE_10GKR
Perhaps PHY_INTERFACE_MODE_10GKR was not used before because Backplane
support was not available and all 10GBase-R family of interfaces should
be using PHY_INTERFACE_MODE_10GBASER.
In case PHY_INTERFACE_MODE_10GKR was used before, this is probably
incorrect and should be changed for those boards to use the correct phy
connection type: PHY_INTERFACE_MODE_10GBASER.
Moreover now I also introduced a new phy connection type to cover also:
40GBase-KR4 which is 40G Backplane over 4-lanes:
	PHY_INTERFACE_MODE_40GKR4

Prior to adding backplane support, 10GKR case was handled the same as
10GBASER in phylink_parse_mode. 
But now because we are adding support for backplane modes, all backplane
phy connection types (like: 10GKR, 40GKR4) must be treated separately to
correctly setup the supported phylink.

Florin.