net: dsa: mv88e6xxx: Default ports 9/10 6390X CMODE to 1000BaseX

The 6390X family has 8 SERDES interfaces. This allows ports 9 and 10
to support up to 10Gbps using 4 SERDES interfaces. However, when lower
speeds are used, which need fewer SERDES interfaces, the unused SERDES
interfaces can be used by ports 2-8.

The hardware defaults to ports 9 and 10 having all 4 SERDES interfaces
assigned to them. This only gets changed when the interface is
configured after what the SFP supports has been determined, or the 10G
PHY completes auto-neg.

For hardware designs which limit ports 9 and 10 to one or two SERDES
interfaces, and place SFPs on the lower interfaces, this is too
late. Those ports with SFP should not wait until ports 9/10 are up in
order to get access to the SERDES interface. So change the default
configuration when the driver is initialised. Configure ports 9 and 10
to 1000BaseX, so they use a single SERDES interface, freeing up the
others. They can steal them back if they need them.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 3 deletions

diff --git a/drivers/net/dsa/mv88e6xxx/port.c b/drivers/net/dsa/mv88e6xxx/port.c
index e718404a5e03..ebd26b6a93e6 100644
--- a/drivers/net/dsa/mv88e6xxx/port.c
+++ b/drivers/net/dsa/mv88e6xxx/port.c
@@ -368,12 +368,15 @@ int mv88e6390x_port_set_cmode(struct mv88e6xxx_chip *chip, int port,
         u16 reg;
         int err;
 
-        if (mode == PHY_INTERFACE_MODE_NA)
-                return 0;
-
         if (port != 9 && port != 10)
                 return -EOPNOTSUPP;
 
+        /* Default to a slow mode, so freeing up SERDES interfaces for
+         * other ports which might use them for SFPs.
+         */
+        if (mode == PHY_INTERFACE_MODE_NA)
+                mode = PHY_INTERFACE_MODE_1000BASEX;
+
         switch (mode) {
         case PHY_INTERFACE_MODE_1000BASEX:
                 cmode = MV88E6XXX_PORT_STS_CMODE_1000BASE_X;