[PATCH net v2] net: dsa: motorcomm: Isolate all ports during chip setup

[David Yang <mmyangfl@gmail.com>]

The chip setup only blocked unknown unicast and unknown multicast
frames, known multicast and broadcast were left open (though the former
cannot appear while the FDB is still empty). Before port_setup() runs,
broadcast frames received on a port flood out of the other ports.

Close the window by fully isolating every port right after the hardware
reset.

Fixes: 186623f4aa72 ("net: dsa: yt921x: Add support for Motorcomm YT921x")
Signed-off-by: David Yang <mmyangfl@gmail.com>
---
v2:
 - reword and reduce code changes
v1: https://lore.kernel.org/r/20261024144023.1010237-1-mmyangfl@gmail.com
 drivers/net/dsa/motorcomm/chip.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/net/dsa/motorcomm/chip.c b/drivers/net/dsa/motorcomm/chip.c
index d4fc20c52a58..08a880867ee1 100644
--- a/drivers/net/dsa/motorcomm/chip.c
+++ b/drivers/net/dsa/motorcomm/chip.c
@@ -2221,6 +2221,7 @@ static int yt921x_chip_reset(struct yt921x_priv *priv)
 {
 	struct device *dev = yt921x_priv_to_device(priv);
 	u16 eth_p_tag;
+	u32 ctrl;
 	u32 val;
 	int res;
 
@@ -2258,6 +2259,17 @@ static int yt921x_chip_reset(struct yt921x_priv *priv)
 		return -EINVAL;
 	}
 
+	/* Block all traffic as soon as we reset the hardware since it now acts
+	 * as a dump switch.
+	 */
+	for (int port = 0; port < YT921X_PORT_NUM; port++) {
+		ctrl = ~(u32)0;
+		res = yt921x_reg_write(priv, YT921X_PORTn_ISOLATION(port),
+				       ctrl);
+		if (res)
+			return res;
+	}
+
 	return 0;
 }
 
-- 
2.53.0