linux-kernel - Re: [RFC 0/4] net: l2switch: Provide support for L2 switch on i.MX28 SoC

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Date:   Fri, 27 Nov 2020 10:16:15 +0100
From:   Lukasz Majewski <lukma@...x.de>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Vladimir Oltean <olteanv@...il.com>,
        Fugang Duan <fugang.duan@....com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        Fabio Estevam <festevam@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Florian Fainelli <f.fainelli@...il.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Peng Fan <peng.fan@....com>, stefan.agner@...adex.com,
        krzk@...nel.org, Shawn Guo <shawnguo@...nel.org>
Subject: Re: [RFC 0/4] net: l2switch: Provide support for L2 switch on
 i.MX28 SoC

Hi Andrew,

> > (A side question - DSA uses switchdev, so when one shall use
> > switchdev standalone?)  
> 
> DSA gives you a framework for an Ethernet switch connected to a host
> via Ethernet for the data plane. Generally, that Ethernet link to the
> switch is a MAC to MAC connection. It can be PHY to PHY. But those are
> just details. The important thing is you use an Ethernet driver on the
> host.
> 
> If you look at pure switchdev devices, they generally DMA frames
> directly into the switch. There is either one DMA queue per switch
> port, or there is a way to multiplex frames over one DMA queue,
> generally by additional fields in the buffer descriptor.
> 
> For this device, at the moment, it is hard to say which is the best
> fit. A lot will depend on how the FEC driver works, if you can reuse
> it, while still having the degree of control you need over the DMA
> channel. If you can reuse the FEC driver, then a DSA driver might
> work. If the coupling it too loose, and you have to take control of
> the DMA, then a pure switchdev driver seems more appropriate.
> 
>     Andrew
> 

Thanks for the detailed explanation.


Best regards,

Lukasz Majewski

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