Merge branch 'net-dsa-fix-chip-wide-frame-size-config-in-some-drivers'

Martin Willi says:

====================
net: dsa: Fix chip-wide frame size config in some drivers

Some DSA chips support a chip-wide frame size configurations, only. Some
drivers adjust that chip-wide setting for user port changes, overriding
the frame size requirements on the CPU port that includes tagger overhead.

Fix the mv88e6xxx and b53 drivers and align them to the behavior of other
drivers.

v2:
  - Skip chip-wide config for non-CPU ports instead of finding the maximim
    MTU over all ports
  - Add a patch fixing the b53 driver as well

v1: https://lore.kernel.org/netdev/[email protected]/
====================

Link: https://patch.msgid.link/[email protected]
Signed-off-by: Paolo Abeni <[email protected]>

Author: Paolo Abeni

drivers/net/dsa/b53/b53_common.c

@@ -2256,6 +2256,9 @@ static int b53_change_mtu(struct dsa_switch *ds, int port, int mtu)
 	if (is5325(dev) || is5365(dev))
 		return -EOPNOTSUPP;
 
+	if (!dsa_is_cpu_port(ds, port))
+		return 0;
+
 	enable_jumbo = (mtu >= JMS_MIN_SIZE);
 	allow_10_100 = (dev->chip_id == BCM583XX_DEVICE_ID);
 

drivers/net/dsa/mv88e6xxx/chip.c

@@ -3626,7 +3626,8 @@ static int mv88e6xxx_change_mtu(struct dsa_switch *ds, int port, int new_mtu)
 	mv88e6xxx_reg_lock(chip);
 	if (chip->info->ops->port_set_jumbo_size)
 		ret = chip->info->ops->port_set_jumbo_size(chip, port, new_mtu);
-	else if (chip->info->ops->set_max_frame_size)
+	else if (chip->info->ops->set_max_frame_size &&
+		 dsa_is_cpu_port(ds, port))
 		ret = chip->info->ops->set_max_frame_size(chip, new_mtu);
 	mv88e6xxx_reg_unlock(chip);