Subject: Re: [PATCH net-next 2/3] net: dsa: Allow default tag protocol to be overridden from DT

From: Andrew Lunn <[email-masked]>
Date: Mon, 29 Mar 2021 00:04:39 +0200

On Mon, Mar 29, 2021 at 12:53:09AM +0300, Vladimir Oltean wrote:
> On Sun, Mar 28, 2021 at 05:52:43PM +0200, Andrew Lunn wrote:
> > > +static int dsa_switch_setup_tag_protocol(struct dsa_switch *ds)
> > > +{
> > > +	const struct dsa_device_ops *tag_ops = ds->dst->tag_ops;
> > > +	struct dsa_switch_tree *dst = ds->dst;
> > > +	int port, err;
> > > +
> > > +	if (tag_ops->proto == dst->default_proto)
> > > +		return 0;
> > > +
> > > +	if (!ds->ops->change_tag_protocol) {
> > > +		dev_err(ds->dev, "Tag protocol cannot be modified\n");
> > > +		return -EINVAL;
> > > +	}
> > > +
> > > +	for (port = 0; port < ds->num_ports; port++) {
> > > +		if (!(dsa_is_dsa_port(ds, port) || dsa_is_cpu_port(ds, port)))
> > > +			continue;
> > 
> > dsa_is_dsa_port() is interesting. Do we care about the tagging
> > protocol on DSA ports? We never see that traffic?
> 
> I believe this comes from me (see dsa_switch_tag_proto_match). I did not
> take into consideration at that time the fact that Marvell switches can
> translate between DSA and EDSA. So I assumed that every switch in the
> tree needs a notification about the tagging protocol, not just the
> top-most one.

Hi Vladimir

static int mv88e6xxx_setup_port_mode(struct mv88e6xxx_chip *chip, int port)
{
        if (dsa_is_dsa_port(chip->ds, port))
                return mv88e6xxx_set_port_mode_dsa(chip, port);

So DSA ports, the ports connecting two switches together, are hard
coded to use DSA.

        if (dsa_is_user_port(chip->ds, port))
                return mv88e6xxx_set_port_mode_normal(chip, port);

        /* Setup CPU port mode depending on its supported tag format */
        if (chip->info->tag_protocol == DSA_TAG_PROTO_DSA)
                return mv88e6xxx_set_port_mode_dsa(chip, port);

        if (chip->info->tag_protocol == DSA_TAG_PROTO_EDSA)
                return mv88e6xxx_set_port_mode_edsa(chip, port);

CPU ports can be configured to DSA or EDSA.

The switches seem happy to translate between DSA and EDSA as needed.

    Andrew