With every port fully isolated during chip setup, the CPU port already
gets its one-way isolation (drop all packets without tag) there, so the
dedicated handling in port_setup() is redundant. Skip the isolation
write for CPU ports in yt921x_userport_standalone(), which port_setup()
also runs for CPU ports, to keep it intact.

Consequently the CPU ports no longer need to be excluded from the
unknown unicast filtering: frames entering a CPU port without a tag are
now dropped by the port isolation instead of the ACT_UNK action.

Signed-off-by: David Yang <mmyangfl@gmail.com>
---
 drivers/net/dsa/motorcomm/chip.c | 46 ++++++--------------------------
 1 file changed, 8 insertions(+), 38 deletions(-)

diff --git a/drivers/net/dsa/motorcomm/chip.c b/drivers/net/dsa/motorcomm/chip.c
index e1fa82c6db95..fb993cc9607c 100644
--- a/drivers/net/dsa/motorcomm/chip.c
+++ b/drivers/net/dsa/motorcomm/chip.c
@@ -1164,10 +1164,13 @@ static int yt921x_userport_standalone(struct yt921x_priv *priv, int port)
 	u32 ctrl;
 	int res;
 
-	ctrl = ~priv->cpu_ports_mask;
-	res = yt921x_reg_write(priv, YT921X_PORTn_ISOLATION(port), ctrl);
-	if (res)
-		return res;
+	if (!(BIT(port) & priv->cpu_ports_mask)) {
+		ctrl = ~priv->cpu_ports_mask;
+		res = yt921x_reg_write(priv, YT921X_PORTn_ISOLATION(port),
+				       ctrl);
+		if (res)
+			return res;
+	}
 
 	/* Turn off FDB learning to prevent FDB pollution */
 	mask = YT921X_PORT_LEARN_DIS;
@@ -1942,8 +1945,6 @@ yt921x_dsa_phylink_get_caps(struct dsa_switch *ds, int port,
 
 static int yt921x_port_setup(struct yt921x_priv *priv, int port)
 {
-	struct dsa_switch *ds = &priv->ds;
-	u32 ctrl;
 	int res;
 
 	res = yt921x_userport_standalone(priv, port);
@@ -1957,27 +1958,6 @@ static int yt921x_port_setup(struct yt921x_priv *priv, int port)
 	if (res)
 		return res;
 
-	if (dsa_is_cpu_port(ds, port)) {
-		/* Egress of CPU port is supposed to be completely controlled
-		 * via tagging, so set to oneway isolated (drop all packets
-		 * without tag).
-		 */
-		ctrl = ~(u32)0;
-		res = yt921x_reg_write(priv, YT921X_PORTn_ISOLATION(port),
-				       ctrl);
-		if (res)
-			return res;
-
-		/* To simplify FDB "isolation" simulation, we also disable
-		 * learning on the CPU port, and let software identify packets
-		 * towarding CPU (either trapped or a static FDB entry is
-		 * matched, no matter which bridge that entry is for), which is
-		 * already done by yt921x_userport_standalone(). As a result,
-		 * VLAN-awareness becomes unrelated on the CPU port (set to
-		 * VLAN-unaware by the way).
-		 */
-	}
-
 	return 0;
 }
 
@@ -2276,10 +2256,8 @@ static int yt921x_chip_reset(struct yt921x_priv *priv)
 static int yt921x_chip_setup_dsa(struct yt921x_priv *priv)
 {
 	struct dsa_switch *ds = &priv->ds;
-	unsigned long cpu_ports_mask;
 	u32 ctrls[2];
 	u32 ctrl;
-	int port;
 	int res;
 
 	/* Enable DSA */
@@ -2297,7 +2275,7 @@ static int yt921x_chip_setup_dsa(struct yt921x_priv *priv)
 	if (res)
 		return res;
 
-	ctrl = GENMASK(10, 0);
+	ctrl = GENMASK(10, 0) & ~priv->cpu_ports_mask;
 	res = yt921x_reg_write(priv, YT921X_FILTER_UNK_UCAST, ctrl);
 	if (res)
 		return res;
@@ -2320,14 +2298,6 @@ static int yt921x_chip_setup_dsa(struct yt921x_priv *priv)
 	ctrl = 0;
 	for (int i = 0; i < YT921X_PORT_NUM; i++)
 		ctrl |= YT921X_ACT_UNK_ACTn_TRAP(i);
-	/* Except for CPU ports, if any packets are sent via CPU ports without
-	 * tag, they should be dropped.
-	 */
-	cpu_ports_mask = priv->cpu_ports_mask;
-	for_each_set_bit(port, &cpu_ports_mask, YT921X_PORT_NUM) {
-		ctrl &= ~YT921X_ACT_UNK_ACTn_M(port);
-		ctrl |= YT921X_ACT_UNK_ACTn_DROP(port);
-	}
 	res = yt921x_reg_write(priv, YT921X_ACT_UNK_UCAST, ctrl);
 	if (res)
 		return res;
-- 
2.53.0