[PATCH V3 1/4 net] net: dsa: b53: deal with Northstar devices using CPU port 5 or 7

["Rafał Miłecki" <zajec5@gmail.com>]

From: Rafał Miłecki <rafal@milecki.pl>

Northstar devices have 3 CPU ports. Ports 5 and 7 may be used but have
their limitations. Warn user when CPU port 8 isn't used and add EAP
setup workaround to avoid non-functional standalone ports.

Fixes: 4227ea91e265 ("net: dsa: b53: prevent standalone from trying to forward to other ports")
Cc: Semih Baskan <strst.gs@gmail.com>
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Tested-by: Semih Baskan <strst.gs@gmail.com>
---
This fixes a regression so it's a net.git material

V2: Print warning on switch setup instead of on actual EAP mode change
V3: Proper subject prefix & shorter comments (long one comes with 2/2)

 drivers/net/dsa/b53/b53_common.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/net/dsa/b53/b53_common.c b/drivers/net/dsa/b53/b53_common.c
index 3f5b9592794d..5fd8362d0430 100644
--- a/drivers/net/dsa/b53/b53_common.c
+++ b/drivers/net/dsa/b53/b53_common.c
@@ -332,6 +332,14 @@ static void b53_set_eap_mode(struct b53_device *dev, int port, int mode)
 {
 	u64 eap_conf;
 
+	/*
+	 * On Northstar setting EAP_MODE_SIMPLIFIED with CPU port 5/7 breaks
+	 * standalone ports, see:
+	 * https://lore.kernel.org/netdev/ce4d9b7b-aaf6-4796-94fb-8c3d6a1dcd4d@gmail.com/
+	 */
+	if (is5301x(dev) && !dsa_is_cpu_port(dev->ds, B53_CPU_PORT))
+		return;
+
 	if (is5325(dev) || is5365(dev) || dev->chip_id == BCM5389_DEVICE_ID)
 		return;
 
@@ -1281,6 +1289,10 @@ static int b53_setup(struct dsa_switch *ds)
 	u16 pvid;
 	int ret;
 
+	/* Discourage users from using port 5 or 7 due to limited features */
+	if (is5301x(dev) && !dsa_is_cpu_port(dev->ds, B53_CPU_PORT))
+		dev_warn(dev->dev, "switch to CPU port 8 to use all switch features\n");
+
 	/* Request bridge PVID untagged when DSA_TAG_PROTO_NONE is set
 	 * which forces the CPU port to be tagged in all VLANs.
 	 */
-- 
2.51.0