net: phy: Create sysfs reciprocal links for attached_dev/phydev

There is currently no way for a program scanning /sys to know whether a
network device is attached to a particular PHY device, just like the PHY
device is not pointed back to its attached network device.

Create a symbolic link in the network device's namespace named "phydev"
which points to the PHY device and create a symbolic link in the PHY
device's namespace named "attached_dev" that points back to the network
device. These links are set up during phy_attach_direct() and removed
during phy_detach() for symetry.
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/phy_device.c

@@ -960,6 +960,15 @@ int phy_attach_direct(struct net_device *dev, struct phy_device *phydev,
 
 	phydev->attached_dev = dev;
 	dev->phydev = phydev;
+	err = sysfs_create_link(&phydev->mdio.dev.kobj, &dev->dev.kobj,
+				"attached_dev");
+	if (err)
+		goto error;
+
+	err = sysfs_create_link(&dev->dev.kobj, &phydev->mdio.dev.kobj,
+				"phydev");
+	if (err)
+		goto error;
 
 	phydev->dev_flags = flags;
 
@@ -1050,6 +1059,8 @@ void phy_detach(struct phy_device *phydev)
 	struct mii_bus *bus;
 	int i;
 
+	sysfs_remove_link(&dev->dev.kobj, "phydev");
+	sysfs_remove_link(&phydev->mdio.dev.kobj, "attached_dev");
 	phydev->attached_dev->phydev = NULL;
 	phydev->attached_dev = NULL;
 	phy_suspend(phydev);