net: dsa: mv88e6xxx: factorize EEE access

Add a MV88E6XXX_FLAG_EEE flag to describe switch models featuring Energy
Efficient Ethernet. Use it to conditionally support such access in the
common code.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/dsa/mv88e6xxx.c b/drivers/net/dsa/mv88e6xxx.c
index 4f0e047..6aac58b 100644
--- a/drivers/net/dsa/mv88e6xxx.c
+++ b/drivers/net/dsa/mv88e6xxx.c
@@ -1105,6 +1105,9 @@
 	struct mv88e6xxx_priv_state *ps = ds_to_priv(ds);
 	int reg;
 
+	if (!mv88e6xxx_has(ps, MV88E6XXX_FLAG_EEE))
+		return -EOPNOTSUPP;
+
 	mutex_lock(&ps->smi_mutex);
 
 	reg = _mv88e6xxx_phy_read_indirect(ps, port, 16);
@@ -1133,6 +1136,9 @@
 	int reg;
 	int ret;
 
+	if (!mv88e6xxx_has(ps, MV88E6XXX_FLAG_EEE))
+		return -EOPNOTSUPP;
+
 	mutex_lock(&ps->smi_mutex);
 
 	ret = _mv88e6xxx_phy_read_indirect(ps, port, 16);