net: phy: Add phy_standalone sysfs entry

Export a phy_standalone device attribute that is meant to give the
indication that this PHY lacks an attached_dev and its corresponding
sysfs link. The attribute will be created only when the
phy_attach_direct() function will be called with a NULL net_device.
Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/ABI/testing/sysfs-class-net-phydev

@@ -34,3 +34,11 @@ Description:
 		xgmii, moca, qsgmii, trgmii, 1000base-x, 2500base-x, rxaui,
 		xaui, 10gbase-kr, unknown
 
+What:		/sys/class/mdio_bus/<bus>/<device>/phy_standalone
+Date:		May 2019
+KernelVersion:	5.3
+Contact:	netdev@vger.kernel.org
+Description:
+		Boolean value indicating whether the PHY device is used in
+		standalone mode, without a net_device associated, by PHYLINK.
+		Attribute created only when this is the case.

drivers/net/phy/phy_device.c

@@ -1164,6 +1164,16 @@ static void phy_sysfs_create_links(struct phy_device *phydev)
 	phydev->sysfs_links = true;
 }
 
+static ssize_t
+phy_standalone_show(struct device *dev, struct device_attribute *attr,
+		    char *buf)
+{
+	struct phy_device *phydev = to_phy_device(dev);
+
+	return sprintf(buf, "%d\n", !phydev->attached_dev);
+}
+static DEVICE_ATTR_RO(phy_standalone);
+
 /**
  * phy_attach_direct - attach a network device to a given PHY device pointer
  * @dev: network device to attach
@@ -1253,6 +1263,13 @@ int phy_attach_direct(struct net_device *dev, struct phy_device *phydev,
 
 	phy_sysfs_create_links(phydev);
 
+	if (!phydev->attached_dev) {
+		err = sysfs_create_file(&phydev->mdio.dev.kobj,
+					&dev_attr_phy_standalone.attr);
+		if (err)
+			phydev_err(phydev, "error creating 'phy_standalone' sysfs entry\n");
+	}
+
 	phydev->dev_flags = flags;
 
 	phydev->interface = interface;
@@ -1380,6 +1397,11 @@ void phy_detach(struct phy_device *phydev)
 			sysfs_remove_link(&dev->dev.kobj, "phydev");
 		sysfs_remove_link(&phydev->mdio.dev.kobj, "attached_dev");
 	}
+
+	if (!phydev->attached_dev)
+		sysfs_remove_file(&phydev->mdio.dev.kobj,
+				  &dev_attr_phy_standalone.attr);
+
 	phy_suspend(phydev);
 	if (dev) {
 		phydev->attached_dev->phydev = NULL;