netdev - Re: [RFC PATCH 1/6] docs: networking: add the document for DFL Ether Group driver

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Message-ID: <20201102023809.GA10673@yilunxu-OptiPlex-7050>
Date:   Mon, 2 Nov 2020 10:38:09 +0800
From:   Xu Yilun <yilun.xu@...el.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     jesse.brandeburg@...el.com, anthony.l.nguyen@...el.com,
        davem@...emloft.net, kuba@...nel.org, mdf@...nel.org,
        lee.jones@...aro.org, linux-kernel@...r.kernel.org,
        linux-fpga@...r.kernel.org, netdev@...r.kernel.org,
        trix@...hat.com, lgoncalv@...hat.com, hao.wu@...el.com,
        yilun.xu@...el.com
Subject: Re: [RFC PATCH 1/6] docs: networking: add the document for DFL Ether
  Group driver

Hi Andrew:

On Mon, Oct 26, 2020 at 08:14:00PM +0100, Andrew Lunn wrote:
> > > > > Do you really mean PHY? I actually expect it is PCS? 
> > > > 
> > > > For this implementation, yes.
> > > 
> > > Yes, you have a PHY? Or Yes, it is PCS?
> > 
> > Sorry, I mean I have a PHY.
> > 
> > > 
> > > To me, the phylib maintainer, having a PHY means you have a base-T
> > > interface, 25Gbase-T, 40Gbase-T?  That would be an odd and expensive
> > > architecture when you should be able to just connect SERDES interfaces
> > > together.
> 
> You really have 25Gbase-T, 40Gbase-T? Between the FPGA & XL710?
> What copper PHYs are using? 
> 
> > I see your concerns about the SERDES interface between FPGA & XL710.
> 
> I have no concerns about direct SERDES connections. That is the normal
> way of doing this. It keeps it a lot simpler, since you don't have to
> worry about driving the PHYs.
>

I did some investigation and now I have some details.
The term 'PHY' described in Ether Group Spec should be the PCS + PMA, a figure
below for one configuration:

 +------------------------+          +-----------------+
 | Host Side Ether Group  |          |      XL710      |
 |                        |          |                 |
 | +--------------------+ |          |                 |
 | | 40G Ether IP       | |          |                 |
 | |                    | |          |                 |
 | |       +---------+  | |  XLAUI   |                 |
 | | MAC - |PCS - PMA|  | |----------| PMA - PCS - MAC |
 | |       +---------+  | |          |                 |
 +-+--------------------+-+          +-----------------+

Thanks,
Yilun