netdev - Re: Distributed Switch Architecture(DSA)

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Date:	Sun, 20 Jun 2010 16:41:31 +0200
From:	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>
To:	Lennert Buytenhek <buytenh@...tstofly.org>
Cc:	netdev@...r.kernel.org
Subject: Re: Distributed Switch Architecture(DSA)

Lennert Buytenhek <buytenh@...tstofly.org> wrote on 2010/06/19 20:57:39:
>
> On Sat, Jun 19, 2010 at 08:48:31PM +0200, Joakim Tjernlund wrote:
>
> > > > > > Not sure how one would express whether VLAN tags should be stripped
> > > > > > off or not when egressing the HW switch's physical port.
> > > > >
> > > > > If you transmit a packet onto 'lan', it will be sent to the switch chip
> > > > > with an "untagged" DSA tag.  If you transmit a packet onto 'lan.123',
> > > > > it will be sent to the switch chip with a "tagged" DSA tag.  See
> > > > > net/dsa/tag_dsa.c for details.
> > > >
> > > > Ah, now I get it, thanks.
> > > > However, how does this work for LAN to LAN pkgs? LAN1 and LAN2 could be
> > > > in the same VLAN but one is implicit(port) VLAN and the
> > > > other is explicit.
> > >
> > > If you tell the HW switch to forward these packets, they will never
> > > appear at the CPU interface, so the DSA tagging/untagging doesn't enter
> > > the picture.
> >
> > "tell the HW switch"? Doesn't DSA do that already?
>
> Not in its current iteration, as I've explained in previous emails.

Sorry, I didn't quite get that.

>
>
> > If not, what is the point of DSA then if it doesn't use the native
> > forwarding capabilities of the HW switch?
>
> The point is and always was to provide a framework for proper integration
> of hardware switch chips into the Linux kernel.  This framework doesn't
> become useless just because it doesn't already support every single
> hardware feature at this point.

Right, sorry if I sounded a bit harsh.

So DSA currently does a very minimal config of the HW switch to get
things going.
If you want to do something more fancy one has to
add a control plane to DSA which would possibly talk
to a user space app. Is that correct?

>
>
> > > > How do I config the HW switch to do that?
> > >
> > > Tell the switch that the vlan is native on one of the ports but not on
> > > the other.  It's been a while since I looked at the chip docs but there
> > > are ways of doing this.
> >
> > The current DSA impl. does not support this? There should be some
> > way to manage this within the DSA framework.
>
> Have you even tried the DSA code?

Not yet and I don't have any MV HW either :(

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