net: phy: Add phy_interface_is_rgmii helper

RGMII interfaces come in 4 different flavors that the PHY library needs
to care about: regular RGMII (no delays), RGMII with either RX or TX
delay, and both. In order to avoid errors of checking only for one type
of RGMII interface and miss the 3 others, introduce a convenience
function which tests for all values.

Suggested-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/phy.h

@@ -677,6 +677,17 @@ static inline bool phy_is_internal(struct phy_device *phydev)
 	return phydev->is_internal;
 }
 
+/**
+ * phy_interface_is_rgmii - Convenience function for testing if a PHY interface
+ * is RGMII (all variants)
+ * @phydev: the phy_device struct
+ */
+static inline bool phy_interface_is_rgmii(struct phy_device *phydev)
+{
+	return phydev->interface >= PHY_INTERFACE_MODE_RGMII &&
+		phydev->interface <= PHY_INTERFACE_MODE_RGMII_TXID;
+}
+
 /**
  * phy_write_mmd - Convenience function for writing a register
  * on an MMD on a given PHY.