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Date:   Mon, 29 Apr 2019 05:37:52 +0000
From:   "Ong, Boon Leong" <boon.leong.ong@...el.com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     "Voon, Weifeng" <weifeng.voon@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Kweh, Hock Leong" <hock.leong.kweh@...el.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Jose Abreu <joabreu@...opsys.com>
Subject: RE: [PATCH 0/7] net: stmmac: enable EHL SGMII

>-----Original Message-----
>From: Andrew Lunn [mailto:andrew@...n.ch]
>Sent: Thursday, April 25, 2019 11:24 PM
>To: Ong, Boon Leong <boon.leong.ong@...el.com>
>Cc: Voon, Weifeng <weifeng.voon@...el.com>; David S. Miller
><davem@...emloft.net>; netdev@...r.kernel.org; linux-
>kernel@...r.kernel.org; Kweh, Hock Leong <hock.leong.kweh@...el.com>;
>Florian Fainelli <f.fainelli@...il.com>; Maxime Coquelin
><mcoquelin.stm32@...il.com>; Giuseppe Cavallaro
><peppe.cavallaro@...com>; Jose Abreu <joabreu@...opsys.com>
>Subject: Re: [PATCH 0/7] net: stmmac: enable EHL SGMII
>
>> >> > > This patch-set is to enable Ethernet controller (DW Ethernet QoS and
>> >> > > DW Ethernet PCS) with SGMII interface in Elkhart Lake.
>> >> >
>> >> > Can the hardware also do 1000BaseX?
>> >>
>> >> Yes, it is able to do 1000BaseX.
>> >
>> >I Voon
>> >
>> >That means you should not really hard code it to SGMII. Somebody is
>> >going to connect an SFP or an Ethernet switch and want to use
>> >1000BaseX.
>>
>> Hi Andrew,
>>
>> The Ethernet controller consists of two ways to connect to external PHY,
>> RGMII and SGMII. The selection is done through soft strap.
>> The patch-series is to enable SGMII interface. The DW xPCS IP is
>> configured to operate in 1000BASE-X mode. The xPCS IP is external
>> connected through internal PHY interface which presents externally
>> as SGMII interface. To help illustrate the connection:-
>>
>>       <-----------------GBE Controller----------------->|<--External PHY chip-->
>>
>>       +----------+                    +----+          +---+                          +-----------------+
>>       |   EQoS   | <-GMII->|xPCS|<--> | L1 | <-- SGMII --> | External GbE |
>>       |   MAC    |                 |         |       |PHY|                         | PHY Chip        |
>>       +----------+                    +----+          +---+                          +-----------------+
>>
>> In future, we will submit the changes for the RGMII connection that
>> bypasses DW xPCS.
>
>The ASCII art get messed up somewhere.
Sorry for that. 

>
>What you are implementing looks like:
>
>
>       <-----------------GBE Controller------------>|<--External PHY chip-->
>
>       +----------+                    +----+                 +---+
>       |   EQoS   | <-GMII->|xPCS|<--> | L1 | <-- SGMII -->   |PHY|
>       |   MAC    |                    |    |                 +---+
>       +----------+                    +----+
>
>With the Ethernet controller, the MAC connects to the xPCS. Out of the
>xPCS you have a SERDES connection, running the SGMII protocol. That
>connects to external pins of the SoC. These are then connected to a
>copper PHY which also supports SGMII.
>
>What i'm trying to understand is if the following is possible:
>
>       <-----------------GBE Controller------------->|<--External SFP cage/module-->
>
>       +----------+                    +----+                   +---+
>       |   EQoS   | <-GMII->|xPCS|<--> | L1 | <-- 1000BaseX --> |SPF|
>       |   MAC    |                    |    |                   +---+
>       +----------+                    +----+
>
>Rather than use a Copper PHY, an SFP cage+module is used. The same
>SERDES interface is used, but 1000BaseX runs over it.
>
>Generally, an xPCS which can run SGMII can also do 1000BaseX, because
>SGMII is just some Cisco Proprietary extensions to 1000BaseX.
>
>If the xPCS can do 1000BaseX over the SERDES, you should not hard code
>it to SGMII, but allow it to be configured.

Thanks for the review and checking above.

Sorry for the delay, we have checked with hardware/SoC HW architect
and gotten confirmation that the controller can only support SGMII inter-chip
connection. It does not support 1000Base-X. 

In this case, we believe that the current implementation of the DW xPCS
are sufficient. Ok?

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