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

On Sun, Mar 28, 2021 at 05:52:43PM +0200, Andrew Lunn wrote:

quoted

+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.