Re: [PATCH net-next 0/4] net: dsa: b53: Clean up CPU/IMP ports

quoted

That DSA_PORT_TYPE_UNUSED would probably require investigating DSA & b53
behaviour *and* discussing it with DSA maintainer to make sure we don't
abuse that.

How absent are these ports in hardware? For DSA_PORT_TYPE_UNUSED we do
register a devlink port, but if those ports are really not present in
hardware, I'm thinking maybe the easiest way would be to supply a
ds->disabled_port_mask before dsa_register_switch(), and DSA will simply
skip those ports when allocating the dp, the devlink_port etc. So you
will literally have nothing for them.

The basic idea seems O.K, we just need to be careful.

We have code like:

static inline bool dsa_is_dsa_port(struct dsa_switch *ds, int p)
{
	return dsa_to_port(ds, p)->type == DSA_PORT_TYPE_DSA;
}

static inline bool dsa_is_user_port(struct dsa_switch *ds, int p)
{
	return dsa_to_port(ds, p)->type == DSA_PORT_TYPE_USER;
}

dsa_to_port(ds, p) will return NULL, and then bad things will happen.

Maybe it would be safer to add DSA_PORT_TYPE_PHANTOM and do allocate
the dp?

    Andrew