net: dsa: mv88e6xxx: Improve multichip isolation of standalone ports

Given that standalone ports are now configured to bypass the ATU and
forward all frames towards the upstream port, extend the ATU bypass to
multichip systems.

Load VID 0 (standalone) into the VTU with the policy bit set. Since
VID 4095 (bridged) is already loaded, we now know that all VIDs in use
are always available in all VTUs. Therefore, we can safely enable
802.1Q on DSA ports.

Setting the DSA ports' VTU policy to TRAP means that all incoming
frames on VID 0 will be classified as MGMT - as a result, the ATU is
bypassed on all subsequent switches.

With this isolation in place, we are able to support configurations
that are simultaneously very quirky and very useful. Quirky because it
involves looping cables between local switchports like in this
example:

CPU
| .------.
.---0---. | .----0----.
| sw0 | | | sw1 |
'-1-2-3-' | '-1-2-3-4-'
$ @ '---' $ @ % %

We have three physically looped pairs ($, @, and %).

This is very useful because it allows us to run the kernel's
kselftests for the bridge on mv88e6xxx hardware.

Signed-off-by: Tobias Waldekranz <[e-mail]>
Reviewed-by: Vladimir Oltean <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/dsa/mv88e6xxx/chip.c

···
 
 int mv88e6xxx_fid_map(struct mv88e6xxx_chip *chip, unsigned long *fid_bitmap)
 {
-	int i, err;
-	u16 fid;
-
 	bitmap_zero(fid_bitmap, MV88E6XXX_N_FID);
 
-	/* Set every FID bit used by the (un)bridged ports */
-	for (i = 0; i < mv88e6xxx_num_ports(chip); ++i) {
-		err = mv88e6xxx_port_get_fid(chip, i, &fid);
-		if (err)
-			return err;
-
-		set_bit(fid, fid_bitmap);
-	}
-
-	/* Set every FID bit used by the VLAN entries */
+	/* Every FID has an associated VID, so walking the VTU
+	 * will discover the full set of FIDs in use.
+	 */
 	return mv88e6xxx_vtu_walk(chip, mv88e6xxx_fid_map_vlan, fid_bitmap);
 }
 
···
 	if (err)
 		return err;
 
-	/* The reset value 0x000 is used to indicate that multiple address
-	 * databases are not needed. Return the next positive available.
-	 */
-	*fid = find_next_zero_bit(fid_bitmap, MV88E6XXX_N_FID, 1);
+	*fid = find_first_zero_bit(fid_bitmap, MV88E6XXX_N_FID);
 	if (unlikely(*fid >= mv88e6xxx_num_databases(chip)))
 		return -ENOSPC;
 
···
 
 	if (!vlan.valid) {
 		memset(&vlan, 0, sizeof(vlan));
+
+		if (vid == MV88E6XXX_VID_STANDALONE)
+			vlan.policy = true;
 
 		err = mv88e6xxx_atu_new(chip, &vlan.fid);
 		if (err)
···
 	if (err)
 		return err;
 
+	/* On chips that support it, set all downstream DSA ports'
+	 * VLAN policy to TRAP. In combination with loading
+	 * MV88E6XXX_VID_STANDALONE as a policy entry in the VTU, this
+	 * provides a better isolation barrier between standalone
+	 * ports, as the ATU is bypassed on any intermediate switches
+	 * between the incoming port and the CPU.
+	 */
+	if (dsa_is_downstream_port(ds, port) &&
+	    chip->info->ops->port_set_policy) {
+		err = chip->info->ops->port_set_policy(chip, port,
+						MV88E6XXX_POLICY_MAPPING_VTU,
+						MV88E6XXX_POLICY_ACTION_TRAP);
+		if (err)
+			return err;
+	}
+
+	/* User ports start out in standalone mode and 802.1Q is
+	 * therefore disabled. On DSA ports, all valid VIDs are always
+	 * loaded in the VTU - therefore, enable 802.1Q in order to take
+	 * advantage of VLAN policy on chips that supports it.
+	 */
 	err = mv88e6xxx_port_set_8021q_mode(chip, port,
-				MV88E6XXX_PORT_CTL2_8021Q_MODE_DISABLED);
+				dsa_is_user_port(ds, port) ?
+				MV88E6XXX_PORT_CTL2_8021Q_MODE_DISABLED :
+				MV88E6XXX_PORT_CTL2_8021Q_MODE_SECURE);
+	if (err)
+		return err;
+
+	/* Bind MV88E6XXX_VID_STANDALONE to MV88E6XXX_FID_STANDALONE by
+	 * virtue of the fact that mv88e6xxx_atu_new() will pick it as
+	 * the first free FID. This will be used as the private PVID for
+	 * unbridged ports. Shared (DSA and CPU) ports must also be
+	 * members of this VID, in order to trap all frames assigned to
+	 * it to the CPU.
+	 */
+	err = mv88e6xxx_port_vlan_join(chip, port, MV88E6XXX_VID_STANDALONE,
+				       MV88E6XXX_G1_VTU_DATA_MEMBER_TAG_UNMODIFIED,
+				       false);
 	if (err)
 		return err;
 
···
 	 * relying on their port default FID.
 	 */
 	err = mv88e6xxx_port_vlan_join(chip, port, MV88E6XXX_VID_BRIDGED,
-				       MV88E6XXX_G1_VTU_DATA_MEMBER_TAG_UNTAGGED,
+				       MV88E6XXX_G1_VTU_DATA_MEMBER_TAG_UNMODIFIED,
 				       false);
 	if (err)
 		return err;

include/net/dsa.h

···
 	return port == dsa_upstream_port(ds, port);
 }
 
+/* Return true if this is a DSA port leading away from the CPU */
+static inline bool dsa_is_downstream_port(struct dsa_switch *ds, int port)
+{
+	return dsa_is_dsa_port(ds, port) && !dsa_is_upstream_port(ds, port);
+}
+
 /* Return the local port used to reach the CPU port */
 static inline unsigned int dsa_switch_upstream_port(struct dsa_switch *ds)
 {