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

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Date:	Sat, 4 Oct 2008 12:22:37 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Lennert Buytenhek <buytenh@...tstofly.org>
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

Lennert Buytenhek wrote:
> 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.

If it's just another protocol then put dsa_ptr along with the other
protocol pointers (ip_ptr etc.).

For those drivers that work with the original DSA tagging format, it's
apparently not just another protocol.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.
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