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

+Russell,

On 6/4/2019 11:58 AM, Voon Weifeng wrote:

quoted

From: Ong Boon Leong <redacted>

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