[EXT] Re: [PATCH v1 2/5] net: phy: marvell: extend 88E2110 to use both 2.5GHz modes

[Kostya Porotchkin]

Hi, Marek,

> -----Original Message-----
> From: Marek Behun <marek.behun at nic.cz>
> Sent: Wednesday, March 24, 2021 13:47
> To: Kostya Porotchkin <kostap at marvell.com>
> Cc: Stefan Roese <sr at denx.de>; u-boot at lists.denx.de; Stefan Chulski
> <stefanc at marvell.com>; Ramon Fried <rfried.dev at gmail.com>; Nadav Haklai
> <nadavh at marvell.com>; Joe Hershberger <joe.hershberger at ni.com>; Marcin
> Wojtas <mw at semihalf.com>; sa_ip-sw-jenkins <sa_ip-sw-
> jenkins at marvell.com>; Igal Liberman <igall at marvell.com>; Simon Glass
> <sjg at chromium.org>; Yan Markman <ymarkman at marvell.com>
> Subject: Re: [EXT] Re: [PATCH v1 2/5] net: phy: marvell: extend 88E2110 to use
> both 2.5GHz modes
> 
> On Wed, 24 Mar 2021 09:55:04 +0000
> Kostya Porotchkin <kostap at marvell.com> wrote:
> 
> > Hi, Marek,
> >
> > > -----Original Message-----
> > > From: Marek Behun <marek.behun at nic.cz>
> > > Sent: Wednesday, March 24, 2021 12:44
> > > To: Stefan Roese <sr at denx.de>
> > > Cc: u-boot at lists.denx.de; Kostya Porotchkin <kostap at marvell.com>;
> > > Stefan Chulski <stefanc at marvell.com>; Ramon Fried
> > > <rfried.dev at gmail.com>; Nadav Haklai <nadavh at marvell.com>; Joe
> > > Hershberger <joe.hershberger at ni.com>; Marcin Wojtas
> > > <mw at semihalf.com>; sa_ip-sw- jenkins <sa_ip-sw-jenkins at marvell.com>;
> > > Igal Liberman <igall at marvell.com>; Simon Glass <sjg at chromium.org>;
> > > Yan Markman <ymarkman at marvell.com>
> > > Subject: [EXT] Re: [PATCH v1 2/5] net: phy: marvell: extend 88E2110
> > > to use both 2.5GHz modes
> > >
> > > External Email
> > >
> > > --------------------------------------------------------------------
> > > --
> > > On Wed, 24 Mar 2021 10:20:05 +0100
> > > Stefan Roese <sr at denx.de> wrote:
> > >
> > > > PHY_INTERFACE_MODE_SGMII_2500
> > >
> > > What the hell is this mode???
> > >
> > > AFAIK something like this does not actually exist.
> > [KP] I think you are wrong. These modes are definitely exist
> > https://urldefense.proofpoint.com/v2/url?u=https-3A__en.wikipedia.org_
> > wiki_2.5GBASE-2DT-5Fand-5F5GBASE-
> 2DT&d=DwICAg&c=nKjWec2b6R0mOyPaz7xtfQ
> > &r=-
> N9sN4p5NSr0JGQoQ_2UCOgAqajG99W1EbSOww0WU8o&m=SCz6AxibFIYZS7
> OKXvlPK
> >
> CJvtAUaDPOmYRpvSNR3jv4&s=R_4D7fksFwBgE8_2RMOIyt5hIs8vgXjimR3E4O
> FUXeU&e
> > =
> >
> > Regards
> > Kosta
> 
> Hi Kosta,
> 
> the wikipedia page you linked specifies copper modes, not PHY modes.
> 
> We are discussing PHY modes here.
[KP] Ahh, sorry, mea culpa.
I think Stefan has some answers to your questions.

Regards
Kosta
> 
> What I am confused about is that this patch adds check for
>   PHY_INTERFACE_MODE_SGMII_2500
> in addition to
>   PHY_INTERFACE_MODE_2500BASEX
> 
> But what is the difference between these two?
> 
> Marvell named this protocol HS-SGMII in some of their datasheets and code. I
> guess this was done because of the similarities with 1000base-x and SGMII.
> Marvell uses the names SGMII and 1000base-x interchangably, although this is
> not correct. I guess they are similarily using names 2500base-x and HS-SGMII
> (and now SGMII_2500) interchangably, which is also not correct.
> 
> SGMII uses the same coding as 1000base-x, but the latter works only with one
> speed (1000mbps), while the former can also work in 10mbps and 100mbps (by
> repeating each byte 100 or 10 times, respectively).
> 
> Then there is 2500base-x, which is the same as 1000base-x, but with the clock
> being at 2.5x the speed of 1000base-x clock.
> 
> But there is no analogue of the SGMII protocol (i.e. the repearing of bytes in
> order to achieve lower speed) for the 2500base-x.
> 
> So what I am confused about here is what is supposed to be the difference
> between
>   PHY_INTERFACE_MODE_SGMII_2500
> and
>   PHY_INTERFACE_MODE_2500BASEX
> ?
> 
> Marek