netdev - Re: [PATCH 3/6] [NET] dsa: add support for original DSA tagging format

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Date:	Fri, 3 Oct 2008 21:32:51 +0200
From:	Lennert Buytenhek <buytenh@...tstofly.org>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	netdev@...r.kernel.org, Byron Bradley <byron.bbradley@...il.com>,
	Jesper Dangaard Brouer <jdb@...x.dk>,
	Tim Ellis <tim.ellis@....com>,
	Andy Fleming <afleming@...escale.com>,
	Imre Kaloz <kaloz@...nwrt.org>, Nicolas Pitre <nico@....org>,
	Dirk Teurlings <dirk@...xia.nl>,
	Peter van Valderen <p.v.valderen@...il.com>
Subject: Re: [PATCH 3/6] [NET] dsa: add support for original DSA tagging format

On Fri, Oct 03, 2008 at 06:25:59PM +0100, Ben Hutchings wrote:

> > Most of the DSA switches currently in the field do not support the
> > Ethertype DSA tagging format that one of the previous patches added
> > support for, but only the original DSA tagging format.
> > 
> > The original DSA tagging format carries the same information as the
> > Ethertype DSA tagging format, but with the difference that it does not
> > have an ethertype field.  In other words, when receiving a packet that
> > is tagged with an original DSA tag, there is no way of telling in
> > eth_type_trans() that this packet is in fact a DSA-tagged packet.
> > 
> > This patch adds a hook into eth_type_trans() which is only compiled in
> > if support for a switch chip that doesn't support Ethertype DSA is
> > selected, and which checks whether there is a DSA switch driver
> > instance attached to this network device which uses the old tag format.
> > If so, it sets the protocol field to ETH_P_DSA without looking at the
> > packet, so that the packet ends up in the right place.
> [...]
> 
> Why should this go in eth_type_trans()?  Why don't you put the hook into
> the specific network driver(s) that need it?
> 
> For that matter, why should dsa_ptr go in struct net_device and not in
> the private state for the specific network drivers that need it?

DSA is just another protocol.  Putting hooks in specific network driver
to handle a certain protocol doesn't seem like the right thing to do to
me.
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