netdev - RE: [PATCH net-next v6 2/5] net: stmmac: introducing support for DWC xPCS logics

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Date:   Wed, 5 Jun 2019 13:13:22 +0000
From:   Jose Abreu <Jose.Abreu@...opsys.com>
To:     Florian Fainelli <f.fainelli@...il.com>,
        Voon Weifeng <weifeng.voon@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Maxime Coquelin" <mcoquelin.stm32@...il.com>,
        Russell King <linux@...linux.org.uk>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Giuseppe Cavallaro" <peppe.cavallaro@...com>,
        Andrew Lunn <andrew@...n.ch>,
        Alexandre Torgue <alexandre.torgue@...com>,
        biao huang <biao.huang@...iatek.com>,
        Ong Boon Leong <boon.leong.ong@...el.com>,
        "Kweh Hock Leong" <hock.leong.kweh@...el.com>
Subject: RE: [PATCH net-next v6 2/5] net: stmmac: introducing support for
 DWC xPCS logics

From: Florian Fainelli <f.fainelli@...il.com>

> +Russell,
> 
> On 6/4/2019 11:58 AM, Voon Weifeng wrote:
> > From: Ong Boon Leong <boon.leong.ong@...el.com>
> > 
> > xPCS is DWC Ethernet Physical Coding Sublayer that may be integrated
> > into a GbE controller that uses DWC EQoS MAC controller. An example of
> > HW configuration is shown below:-
> > 
> >   <-----------------GBE Controller---------->|<--External PHY chip-->
> > 
> >   +----------+         +----+    +---+               +--------------+
> >   |   EQoS   | <-GMII->| DW |<-->|PHY| <-- SGMII --> | External GbE |
> >   |   MAC    |         |xPCS|    |IF |               | PHY Chip     |
> >   +----------+         +----+    +---+               +--------------+
> >          ^               ^                                  ^
> >          |               |                                  |
> >          +---------------------MDIO-------------------------+
> > 
> > xPCS is a Clause-45 MDIO Manageable Device (MMD) and we need a way to
> > differentiate it from external PHY chip that is discovered over MDIO.
> > Therefore, xpcs_phy_addr is introduced in stmmac platform data
> > (plat_stmmacenet_data) for differentiating xPCS from 'phy_addr' that
> > belongs to external PHY.
> 
> Assuming this DW xPCS can be found with designs other than STMMAC would
> not it make sense to model this as some kind of PHY/MDIO bridge? A
> little bit like what drivers/net/phy/xilinx_gmii2rgmii.c tries to do?

Yes, DW XPCS is a separate IP that can be sold without the MAC.

Thanks,
Jose Miguel Abreu