[PATCH net-next v4] net: dsa: realtek: rtl8366rb: Fix up port isolation

[Linus Walleij <linusw@kernel.org>]

Sashiko reports that we incorrectly disable isolation in the setup
loop while what we want to do is to enable it.

Enable it by unconditionally setting the enable bit 0 in
rtl8366rb_port_set_isolation() so a mask of 0 when passed in
will enable isolation and isolate from ALL ports.

Fix up the comments so it is clear what is going on, including a
missing word in the helper function.

Reported-by: Paolo Abeni <pabeni@redhat.com>
Closes: https://sashiko.dev/#/patchset/20260630-rtl8366rb-improvements-v2-0-05eb9d6a37f5%40kernel.org
Signed-off-by: Linus Walleij <linusw@kernel.org>
---
Changes in v4:
- Fix the bug by going back to passing 0 (disable forwarding
  to all ports) and just enforcing the enable bit so that
  isolation is turned on with all zeroes in the port mask.
- Link to v3: https://patch.msgid.link/20260725-rtl8366rb-fixes-v3-1-57557b39aaa5@kernel.org

Changes in v3:
- Fixup the erroneous shifted bitmask (I did not have my coffee...)
- Use GENMASK(ds->num_ports - 1, 0) top properly create a bitmask of
  all the ports, and isolate every port from every port.
- Link to v2: https://patch.msgid.link/20260721-rtl8366rb-fixes-v2-1-24464bd1efa4@kernel.org

Changes in v2:
- Properly fix the issue by setting all isolation bits to 1.
- Link to v1: https://patch.msgid.link/20260711-rtl8366rb-fixes-v1-1-12b9210b0cce@kernel.org
---
 drivers/net/dsa/realtek/rtl8366rb.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/net/dsa/realtek/rtl8366rb.c b/drivers/net/dsa/realtek/rtl8366rb.c
index d2fa8ff6a5d0..f11831b66de8 100644
--- a/drivers/net/dsa/realtek/rtl8366rb.c
+++ b/drivers/net/dsa/realtek/rtl8366rb.c
@@ -794,11 +794,10 @@ static int rtl8366rb_setup_all_leds_off(struct realtek_priv *priv)
 static int rtl8366rb_port_set_isolation(struct realtek_priv *priv, int port,
 					u32 mask)
 {
-	/* Bit 0 enables isolation so set this if we enable isolation
-	 * any of the ports an clear it if we disable on all of them.
+	/* Bit 0 enables isolation, the mask indicates allowed forwarding
+	 * ports
 	 */
-	if (mask)
-		mask = RTL8366RB_PORT_ISO_PORTS(mask) | RTL8366RB_PORT_ISO_EN;
+	mask = RTL8366RB_PORT_ISO_PORTS(mask) | RTL8366RB_PORT_ISO_EN;
 
 	return regmap_write(priv->map, RTL8366RB_PORT_ISO(port),
 			    mask);
@@ -974,7 +973,7 @@ static int rtl8366rb_setup(struct dsa_switch *ds)
 		if (!dsa_port_is_user(dp))
 			continue;
 
-		/* Forward only to the CPU */
+		/* Forward only to the CPU(s), isolate from all other ports */
 		ret = rtl8366rb_port_set_isolation(priv, dp->index, upports_mask);
 		if (ret)
 			return ret;

---
base-commit: 23dad2d088dfc82cae1f5a936f8ff7ffebb38dd9
change-id: 20260702-rtl8366rb-fixes-a93f831ec2a4

Best regards,
--  
Linus Walleij <linusw@kernel.org>