net: phy: expose PHY device interface mode

Expose the PHY device interface mode through sysfs since this is an
useful piece of information for knowing how the attached networking
device will have configured its transmit/receive path.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c
index 71e4900..7c66ea0 100644
--- a/drivers/net/phy/mdio_bus.c
+++ b/drivers/net/phy/mdio_bus.c
@@ -432,8 +432,18 @@
 }
 static DEVICE_ATTR_RO(phy_id);
 
+static ssize_t
+phy_interface_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct phy_device *phydev = to_phy_device(dev);
+
+	return sprintf(buf, "%s\n", phy_modes(phydev->interface));
+}
+static DEVICE_ATTR_RO(phy_interface);
+
 static struct attribute *mdio_dev_attrs[] = {
 	&dev_attr_phy_id.attr,
+	&dev_attr_phy_interface.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(mdio_dev);