netdev - RE: [PATCH 1/6] net: phy: add interface modes for XFI, SFI

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Date:   Thu, 19 Dec 2019 21:34:57 +0000
From:   "Madalin Bucur (OSS)" <madalin.bucur@....nxp.com>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "andrew@...n.ch" <andrew@...n.ch>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "hkallweit1@...il.com" <hkallweit1@...il.com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: RE: [PATCH 1/6] net: phy: add interface modes for XFI, SFI

> -----Original Message-----
> From: Russell King - ARM Linux admin <linux@...linux.org.uk>
> Sent: Thursday, December 19, 2019 9:03 PM
> To: Madalin Bucur <madalin.bucur@....com>
> Cc: davem@...emloft.net; netdev@...r.kernel.org; andrew@...n.ch;
> f.fainelli@...il.com; hkallweit1@...il.com; shawnguo@...nel.org;
> devicetree@...r.kernel.org
> Subject: Re: [PATCH 1/6] net: phy: add interface modes for XFI, SFI
> 
> On Thu, Dec 19, 2019 at 06:32:51PM +0000, Madalin Bucur wrote:
> > > -----Original Message-----
> > > From: Russell King - ARM Linux admin <linux@...linux.org.uk>
> > > Sent: Thursday, December 19, 2019 7:29 PM
> > > To: Madalin Bucur <madalin.bucur@....com>
> > > Cc: davem@...emloft.net; netdev@...r.kernel.org; andrew@...n.ch;
> > > f.fainelli@...il.com; hkallweit1@...il.com; shawnguo@...nel.org;
> > > devicetree@...r.kernel.org
> > > Subject: Re: [PATCH 1/6] net: phy: add interface modes for XFI, SFI
> > >
> > > On Thu, Dec 19, 2019 at 05:21:16PM +0200, Madalin Bucur wrote:
> > > > From: Madalin Bucur <madalin.bucur@....com>
> > > >
> > > > Add explicit entries for XFI, SFI to make sure the device
> > > > tree entries for phy-connection-type "xfi" or "sfi" are
> > > > properly parsed and differentiated against the existing
> > > > backplane 10GBASE-KR mode.
> > >
> > > 10GBASE-KR is actually used for XFI and SFI (due to a slight mistake
> on
> > > my part, it should've been just 10GBASE-R).
> > >
> > > Please explain exactly what the difference is between XFI, SFI and
> > > 10GBASE-R. I have not been able to find definitive definitions for
> > > XFI and SFI anywhere, and they appear to be precisely identical to
> > > 10GBASE-R. It seems that it's just a terminology thing, with
> > > different groups wanting to "own" what is essentially exactly the
> > > same interface type.
> >
> > Hi Russell,
> >
> > 10GBase-R could be used as a common nominator but just as well 10G and
> > remove the rest while we're at it. There are/may be differences in
> > features, differences in the way the HW is configured (the most
> > important aspect) and one should be able to determine what interface
> > type is in use to properly configure the HW. SFI does not have the CDR
> > function in the PMD, relying on the PMA signal conditioning vs the XFI
> > that requires this in the PMD. We kept the xgmii compatible for so long
> > without much issues until someone started cleaning up the PHY supported
> > modes. Since we're doing that, let's be rigorous. The 10GBase-KR is
> > important too, we have some backplane code in preparation and having it
> > there could pave the way for a simpler integration.
> 
> The problem we currently have is:
> 
> $ grep '10gbase-kr' arch/*/boot/dts -r
> 
> virtually none of those are actually backplane. For the mcbin matches,
> these are either to a 88x3310 PHY for the doubleshot, which dynamically
> operates between XFI, 5GBASE-R, 2500BASE-X, or SGMII according to the
> datasheet.

Yes, I've seen it's used already in several places:

$ grep PHY_INTERFACE_MODE_10GKR drivers/net -nr
drivers/net/phy/marvell10g.c:219:       if (iface != PHY_INTERFACE_MODE_10GKR) {
drivers/net/phy/marvell10g.c:307:           phydev->interface != PHY_INTERFACE_MODE_10GKR)
drivers/net/phy/marvell10g.c:389:            phydev->interface == PHY_INTERFACE_MODE_10GKR) && phydev->link) {
drivers/net/phy/marvell10g.c:398:                       phydev->interface = PHY_INTERFACE_MODE_10GKR;
drivers/net/phy/phylink.c:296:          case PHY_INTERFACE_MODE_10GKR:
drivers/net/phy/aquantia_main.c:361:            phydev->interface = PHY_INTERFACE_MODE_10GKR;
drivers/net/phy/aquantia_main.c:499:        phydev->interface != PHY_INTERFACE_MODE_10GKR)
drivers/net/phy/sfp-bus.c:340:          return PHY_INTERFACE_MODE_10GKR;
drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c:1117:   return interface == PHY_INTERFACE_MODE_10GKR ||
drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c:1203:   case PHY_INTERFACE_MODE_10GKR:
drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c:1652:   case PHY_INTERFACE_MODE_10GKR:
drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c:4761:   case PHY_INTERFACE_MODE_10GKR:
drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c:4783:   case PHY_INTERFACE_MODE_10GKR:

We should fix this, if it's incorrect.

> If we add something else, then the problem becomes what to do about
> that lot - one of the problems is, it seems we're going to be breaking
> DT compatibility by redefining 10gbase-kr to be correct.

We need the committer/maintainer to update that to a correct value.
 
> It's interesting to hear what the difference is between XFI and SFI,
> but it's weird that PHYs such as 88x3310 have no configuration of their
> fiber interface to enable or disable the CDR, yet it supports fiber
> interfaces, and explicitly shows applications involving "XFI/SFI".
> There's no mention of the CDR in the datasheet either.

I understand SFI came later, with the advantage of cheaper and less power
consuming SFP+ modules.