netdev - Re: DSA vs. SWTICHDEV ?

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Date:   Wed, 30 Nov 2016 21:43:34 +0100
From:   Jiri Pirko <jiri@...nulli.us>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Joakim Tjernlund <Joakim.Tjernlund@...inera.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: DSA vs. SWTICHDEV ?

Wed, Nov 30, 2016 at 07:09:27PM CET, andrew@...n.ch wrote:
>> Something like that. I need to run routing protocols on the switch I/Fs and egress
>> pkgs on selected switch I/Fs bypassing ARP, just like DSA does with its vendor
>> tags.
>
>Does the switch have an equivalent tagging protocol? If you are
>building a tree of switches you need something like this for frames
>going from the host via intermediate switches and out a specific port
>on a remote switch.
>
>> We might have a tree as well so now I really wonder: Given we write a
>> proper switchdev driver, can it support switchtrees without touching
>> switchdev infra structure?
>
>Jiri Pirko <jiri@...nulli.us> is probably the best person to ask about
>this. DSA hides the knowledge that there is multiple switches. To
>switchdev, a tree of switches looks like one switch. This is not
>because of switchdev, it is just the existing DSA code worked when
>switchdev came along.

Looks like the hw is DSA-ish. If I'm not mistaken about that, should be
handled as a part of DSA.


>
> If not I guess we will attach a physical
>> eth I/F to the switch and use both DSA and switchdev to support both trees
>> and HW offload. 
>
>This only works if the switch has the necessary tagging protocol to
>pass through multiple switches.
>
>> We have on an existing board with a BCM ROBO switch with lots of ports(>24),
>> managed over SPI. Looking at BCM DSA tag code it looks like it only supports
>> some 8 ports or so. I still have to find out if this is a limitation in BCM tagging
>> protocol or if just not impl. in DSA yet.
>
>Hi Florian, care to comment?
>
>As far as i understand, the tag used for SF2 and B53 does not support
>a tree of switches. But the big ROBO switches might have a different
>tagging protocol.
>
>  Andrew