net: dsa: b53: Set correct number of ports in the DSA struct

[ Upstream commit d12e1c4 ]

Setting DSA_MAX_PORTS caused DSA to call b53 callbacks (e.g.
b53_disable_port() during dsa_register_switch()) for invalid
(non-existent) ports. That made b53 modify unrelated registers and is
one of reasons for a broken BCM5301x support.

This problem exists for years but DSA_MAX_PORTS usage has changed few
times. It seems the most accurate to reference commit dropping
dsa_switch_alloc() in the Fixes tag.

Fixes: 7e99e34 ("net: dsa: remove dsa_switch_alloc helper")
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/net/dsa/b53/b53_common.c

@@ -2615,6 +2615,8 @@ static int b53_switch_init(struct b53_device *dev)
 	dev->enabled_ports |= BIT(dev->cpu_port);
 	dev->num_ports = fls(dev->enabled_ports);
 
+	dev->ds->num_ports = min_t(unsigned int, dev->num_ports, DSA_MAX_PORTS);
+
 	/* Include non standard CPU port built-in PHYs to be probed */
 	if (is539x(dev) || is531x5(dev)) {
 		for (i = 0; i < dev->num_ports; i++) {
@@ -2659,7 +2661,6 @@ struct b53_device *b53_switch_alloc(struct device *base,
 		return NULL;
 
 	ds->dev = base;
-	ds->num_ports = DSA_MAX_PORTS;
 
 	dev = devm_kzalloc(base, sizeof(*dev), GFP_KERNEL);
 	if (!dev)