phy: Add set_mode callback

The initial use for this is for PHYs that have a mode related to USB OTG.
There are several SoCs (e.g. TI OMAP and DA8xx) that have a mode setting
in the USB PHY to override OTG VBUS and ID signals.

Of course, the enum can be expaned in the future to include modes for
other types of PHYs as well.

Suggested-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: David Lechner <david@lechnology.com>

drivers/phy/phy-core.c

@@ -342,6 +342,21 @@ int phy_power_off(struct phy *phy)
 }
 EXPORT_SYMBOL_GPL(phy_power_off);
 
+int phy_set_mode(struct phy *phy, enum phy_mode mode)
+{
+	int ret;
+
+	if (!phy || !phy->ops->set_mode)
+		return 0;
+
+	mutex_lock(&phy->mutex);
+	ret = phy->ops->set_mode(phy, mode);
+	mutex_unlock(&phy->mutex);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(phy_set_mode);
+
 /**
  * _of_phy_get() - lookup and obtain a reference to a phy by phandle
  * @np: device_node for which to get the phy