net: dsa: xrs700x: reject unsupported HSR configurations

As discussed here:
https://lore.kernel.org/netdev/20240620090210.drop6jwh7e5qw556@skbuf/

the fact is that the xrs700x.c driver only supports offloading
HSR_PT_SLAVE_A and HSR_PT_SLAVE_B (which were the only port types at the
time the offload was written, _for this driver_).

Up until now, the API did not explicitly tell offloading drivers what
port has what role. So xrs700x can get confused and think that it can
support a configuration which it actually can't. There was a table in
the attached link which gave an example:

$ ip link add name hsr0 type hsr slave1 swp0 slave2 swp1 \
	interlink swp2 supervision 45 version 1

        HSR_PT_SLAVE_A    HSR_PT_SLAVE_B      HSR_PT_INTERLINK
 ----------------------------------------------------------------
 user
 space        0                 1                   2
 requests
 ----------------------------------------------------------------
 XRS700X
 driver       1                 2                   -
 understands

The switch would act as if the ring ports were swp1 and swp2.

Now that we have explicit hsr_get_port_type() API, let's use that to
work around the unintended semantical changes of the offloading API
brought by the introduction of interlink ports in HSR.

Fixes: 5055ccc ("net: hsr: Provide RedBox support (HSR-SAN)")
Cc: Lukasz Majewski <lukma@denx.de>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: George McCollister <george.mccollister@gmail.com>
Link: https://patch.msgid.link/20251130131657.65080-5-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: vladimiroltean

drivers/net/dsa/xrs700x/xrs700x.c

@@ -566,6 +566,7 @@ static int xrs700x_hsr_join(struct dsa_switch *ds, int port,
 	struct xrs700x *priv = ds->priv;
 	struct net_device *user;
 	int ret, i, hsr_pair[2];
+	enum hsr_port_type type;
 	enum hsr_version ver;
 	bool fwd = false;
 
@@ -589,6 +590,16 @@ static int xrs700x_hsr_join(struct dsa_switch *ds, int port,
 		return -EOPNOTSUPP;
 	}
 
+	ret = hsr_get_port_type(hsr, dsa_to_port(ds, port)->user, &type);
+	if (ret)
+		return ret;
+
+	if (type != HSR_PT_SLAVE_A && type != HSR_PT_SLAVE_B) {
+		NL_SET_ERR_MSG_MOD(extack,
+				   "Only HSR slave ports can be offloaded");
+		return -EOPNOTSUPP;
+	}
+
 	dsa_hsr_foreach_port(dp, ds, hsr) {
 		if (dp->index != port) {
 			partner = dp;