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

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Date:   Tue, 27 Oct 2020 11:27:32 +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
Subject: Re: [RFC PATCH 1/6] docs: networking: add the document for DFL Ether
  Group driver

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? 

Sorry for the confusing. I'll check with our board designer and reply
later.

> 
> > 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 about the DSA, and actually I wrote a
> > experimental DSA driver. It works and almost meets my need, I can make
> > configuration, run pktgen on slave inf.
> 
> Cool. As i said, I don't know if this actually needs to be a DSA
> driver. It might just need to borrow some ideas from DSA.
> 
> > Mm.. seems the hardware should be changed, either let host directly
> > access the QSFP, or re-design the BMC to provide more info for QSFP.
> 
> At a minimum, you need to support ethtool -m. It could be a firmware
> call to the BMC, our you expose the i2c bus somehow. There are plenty
> of MAC drivers which implement eththool -m without using phylink.
> 
> But i think you need to take a step back first, and look at the bigger
> picture. What is Intel's goal? Are they just going to sell complete
> cards? Or do they also want to sell the FPGA as a components anybody
> get put onto their own board?
> 
> If there are only ever going to be compete cards, then you can go the
> firmware direction, push a lot of functionality into the BMC, and have
> the card driver make firmware calls to control the SFP, retimer,
> etc. You can then throw away your mdio and phy driver hacks.
> 
> If however, the FPGA is going to be available as a component, can you
> also assume there is a BMC? Running Intel firmware? Can the customer
> also modify this firmware for their own needs? I think that is going
> to be difficult. So you need to push as much as possible towards
> linux, and let Linux drive all the hardware, the SFP, retimer, FPGA,
> etc.

This is a very helpful. I'll share with our team and reconsider about the
design.

Thanks,
Yilun

> 
> 	Andrew
>