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

[Stefan Chulski]

> > > > > 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
> > >
> > > I not sure what is correct naming for these mode. PHY_INTERFACE
> > > includes both MAC2PHY interfaces(MII, RGMII and etc), PHY2PHY
> > > interfaces(like
> > > BASEX) and SGMII(which is kind of both).
> > > For both 2500BASEX and SGMII_2500 Serdes lanes set to HS-SGMII in
> > > 3.125G speed, but MAC configured differently and autoneg cannot be
> supported.
> > >
> > > Regards,
> > > Stefan.
> >
> > Since we already has PHY_INTERFACE_MODE_SGMII and
> > PHY_INTERFACE_MODE_QSGMII (5G mode), maybe we should call
> PHY_INTERFACE_MODE_HSGMII - High-Serial Gigabit Media Independent
> Interface (HSGMII, 3.125Gbps).
> 
> And we have now autonegotiation in this discussion. Just today I sent a
> question to Marvell about 2500base-x and why inband autonegotiation is not
> supported there, while it is for 1000base-x.

To clear thing out, inband autonegotiation is negotiation of pause, speed and duplex over PCS(usually between MAC and PHY).

> So are you saying that 2500base-x mode is like 1000base-x, but at 2.5g speed,
> and without inband autonegotiation?

>From Serdes configurations point of view - lanes configured to 3_125G in 2500base-x and to 1_25G in 1000base-x. 
MAC doesn't support inband autonegotiation in base-x mode.
PHY side still can negotiate pause. 

So: Host side doesn't support inband autoneg(speed/duplex) and speed/duplex fixed. Line side can support autoneg of pause.

> And meanwhile HS-SGMII mode is like SGMII, but at 2.5g speed, and _WITH_
> autonegotiation? And what does this autonegotiation support?

SGMII has inband negotiation of speed and duplex(1000/100/10 - full/half), but since serdes reconfiguration required to switch between HS-SGMII and SGMII.
inband negotiation between 2.5C and 1G not supported.

So for example if you have:

MAC/Serdes set to 2.5G <-> PHY that support negotiation of link and negotiated 1G speed with link partner. Packet processor driver should reconfigure Serdes Lanes speed.

> Does is support only negotiation of Pause? Or does it support negotiation of link 
> duplexicity and speed as well?

In HS-SGMII there no much options speed always 2500 and duplex full, only pause taken from PCS inband Auto-Negotiation.
For SGMII pause, duplexicity and speed negotiation supported. 

Stefan,
Regards.