net: dsa: introduce dsa_towards_port helper

Add a new helper returning the local port used to reach an arbitrary
switch port in the fabric.

Its only user at the moment is the dsa_upstream_port helper, which
returns the local port reaching the dedicated CPU port, but it will be
used in cross-chip FDB operations.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 13 insertions, 10 deletions

diff --git a/include/net/dsa.h b/include/net/dsa.h
index 6700dff46a80..8198efcc8ced 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h
@@ -296,20 +296,23 @@ static inline u32 dsa_user_ports(struct dsa_switch *ds)
         return mask;
 }
 
+/* Return the local port used to reach an arbitrary switch port */
+static inline unsigned int dsa_towards_port(struct dsa_switch *ds, int device,
+                                            int port)
+{
+        if (device == ds->index)
+                return port;
+        else
+                return ds->rtable[device];
+}
+
+/* Return the local port used to reach the dedicated CPU port */
 static inline u8 dsa_upstream_port(struct dsa_switch *ds)
 {
         struct dsa_switch_tree *dst = ds->dst;
+        struct dsa_port *cpu_dp = dst->cpu_dp;
 
-        /*
-         * If this is the root switch (i.e. the switch that connects
-         * to the CPU), return the cpu port number on this switch.
-         * Else return the (DSA) port number that connects to the
-         * switch that is one hop closer to the cpu.
-         */
-        if (dst->cpu_dp->ds == ds)
-                return dst->cpu_dp->index;
-        else
-                return ds->rtable[dst->cpu_dp->ds->index];
+        return dsa_towards_port(ds, cpu_dp->ds->index, cpu_dp->index);
 }
 
 typedef int dsa_fdb_dump_cb_t(const unsigned char *addr, u16 vid,