[PATCH V2 net 1/2] 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>
---
V2: Print warning on switch setup instead of on actual EAP mode change

I added PATCH 2/2 as requested but I'm not sure what DT maintainers will
say about it. I'd suggest to take this fix if there are not more
objections on net changes so regression can be fixed. I believe we can
take more time to improve Linux dealing with switch to be more optimal.

 drivers/net/dsa/b53/b53_common.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/drivers/net/dsa/b53/b53_common.c b/drivers/net/dsa/b53/b53_common.c
index 3f5b9592794d..a9bc90b2ffd2 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;
 
+	/*
+	 * Setting EAP_MODE_SIMPLIFIED with port 5/7 used as CPU port 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 +1289,18 @@ static int b53_setup(struct dsa_switch *ds)
 	u16 pvid;
 	int ret;
 
+	/*
+	 * Northstar SoCs devices have 3 Ethernet controllers and 3 CPU ports:
+	 * 5 (IMP1), 7, 8 (IMP0). This design was meant for dual IMP setups when
+	 * WAN traffic goes to port 5 and LAN traffic goes to port 8.
+	 *
+	 * While all 3 ports support Broadcom header, ports 5 and 7 have their
+	 * limitations. Features that relay on trapping to CPU (e.g. EAP, STP)
+	 * won't work when using those as CPU ones.
+	 */
+	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