drivers: phy: add calibrate method

Some quirky UDCs (like dwc3 on Exynos) need to have their phys calibrated e.g.
for using super speed. This patch adds a new phy_calibrate() method.
When the calibration should be used is dependent on actual chip.

In case of dwc3 on Exynos the calibration must happen after usb_add_hcd()
(while in host mode), because certain phy parameters like Tx LOS levels
and boost levels need to be calibrated further post initialization of xHCI
controller, to get SuperSpeed operations working. But an hcd must be
prepared first in order to pass it to usb_add_hcd(), so, in particular, dwc3
registers must be available first, and in order for the latter to happen
the phys must be initialized. This poses a chicken and egg problem if
the calibration were to be performed in phy_init(). To break the circular
dependency a separate method is added which can be called at a desired
moment after phy intialization.

Signed-off-by: Andrzej Pietrasiewicz <[e-mail]>
Signed-off-by: Kishon Vijay Abraham I <[e-mail]>

drivers/phy/phy-core.c

···
 }
 EXPORT_SYMBOL_GPL(phy_reset);
 
+int phy_calibrate(struct phy *phy)
+{
+	int ret;
+
+	if (!phy || !phy->ops->calibrate)
+		return 0;
+
+	mutex_lock(&phy->mutex);
+	ret = phy->ops->calibrate(phy);
+	mutex_unlock(&phy->mutex);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(phy_calibrate);
+
 /**
  * _of_phy_get() - lookup and obtain a reference to a phy by phandle
  * @np: device_node for which to get the phy

include/linux/phy/phy.h

···
  * @power_off: powering off the phy
  * @set_mode: set the mode of the phy
  * @reset: resetting the phy
+ * @calibrate: calibrate the phy
  * @owner: the module owner containing the ops
  */
 struct phy_ops {
···
 	int	(*power_off)(struct phy *phy);
 	int	(*set_mode)(struct phy *phy, enum phy_mode mode);
 	int	(*reset)(struct phy *phy);
+	int	(*calibrate)(struct phy *phy);
 	struct module *owner;
 };
 
···
 int phy_power_off(struct phy *phy);
 int phy_set_mode(struct phy *phy, enum phy_mode mode);
 int phy_reset(struct phy *phy);
+int phy_calibrate(struct phy *phy);
 static inline int phy_get_bus_width(struct phy *phy)
 {
 	return phy->attrs.bus_width;
···
 }
 
 static inline int phy_reset(struct phy *phy)
+{
+	if (!phy)
+		return 0;
+	return -ENOSYS;
+}
+
+static inline int phy_calibrate(struct phy *phy)
 {
 	if (!phy)
 		return 0;