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>

Documentation/ABI/testing/sysfs-bus-mdio

@@ -7,3 +7,13 @@ Description:
 		by the device during bus enumeration, encoded in hexadecimal.
 		This ID is used to match the device with the appropriate
 		driver.
+
+What:		/sys/bus/mdio_bus/devices/.../phy_interface
+Date:		February 2014
+KernelVersion:	3.15
+Contact:	netdev@vger.kernel.org
+Description:
+		This attribute contains the PHY interface as configured by the
+		Ethernet driver during bus enumeration, encoded in string.
+		This interface mode is used to configure the Ethernet MAC with the
+		appropriate mode for its data lines to the PHY hardware.

drivers/net/phy/mdio_bus.c

@@ -432,8 +432,18 @@ phy_id_show(struct device *dev, struct device_attribute *attr, char *buf)
 }
 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);