net: dsa: microchip: ksz8795: Reject unsupported VLAN configuration

The switches supported by ksz8795 only have a per-port flag for Tag
Removal.  This means it is not possible to support both tagged and
untagged VLANs on the same port.  Reject attempts to add a VLAN that
requires the flag to be changed, unless there are no VLANs currently
configured.

VID 0 is excluded from this check since it is untagged regardless of
the state of the flag.

On the CPU port we could support tagged and untagged VLANs at the same
time.  This will be enabled by a later patch.

Fixes: e66f840c ("net: dsa: ksz: Add Microchip KSZ8795 DSA driver")
Signed-off-by: Ben Hutchings <ben.hutchings@mind.be>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/microchip/ksz8795.c

@@ -1140,13 +1140,38 @@ static int ksz8_port_vlan_add(struct dsa_switch *ds, int port,
 {
 	bool untagged = vlan->flags & BRIDGE_VLAN_INFO_UNTAGGED;
 	struct ksz_device *dev = ds->priv;
+	struct ksz_port *p = &dev->ports[port];
 	u16 data, new_pvid = 0;
 	u8 fid, member, valid;
 
 	if (ksz_is_ksz88x3(dev))
 		return -ENOTSUPP;
 
-	ksz_port_cfg(dev, port, P_TAG_CTRL, PORT_REMOVE_TAG, untagged);
+	/* If a VLAN is added with untagged flag different from the
+	 * port's Remove Tag flag, we need to change the latter.
+	 * Ignore VID 0, which is always untagged.
+	 */
+	if (untagged != p->remove_tag && vlan->vid != 0) {
+		unsigned int vid;
+
+		/* Reject attempts to add a VLAN that requires the
+		 * Remove Tag flag to be changed, unless there are no
+		 * other VLANs currently configured.
+		 */
+		for (vid = 1; vid < dev->num_vlans; ++vid) {
+			/* Skip the VID we are going to add or reconfigure */
+			if (vid == vlan->vid)
+				continue;
+
+			ksz8_from_vlan(dev, dev->vlan_cache[vid].table[0],
+				       &fid, &member, &valid);
+			if (valid && (member & BIT(port)))
+				return -EINVAL;
+		}
+
+		ksz_port_cfg(dev, port, P_TAG_CTRL, PORT_REMOVE_TAG, untagged);
+		p->remove_tag = untagged;
+	}
 
 	ksz8_r_vlan_table(dev, vlan->vid, &data);
 	ksz8_from_vlan(dev, data, &fid, &member, &valid);

drivers/net/dsa/microchip/ksz_common.h

@@ -27,6 +27,7 @@ struct ksz_port_mib {
 struct ksz_port {
 	u16 member;
 	u16 vid_member;
+	bool remove_tag;		/* Remove Tag flag set, for ksz8795 only */
 	int stp_state;
 	struct phy_device phydev;