phy: core: Add documentation of phy operation order

Add documentation on phy function usage: init function must be
called before power_on; power_off must be called before exit.

Signed-off-by: Jules Maselbas <jmaselbas@kalray.eu>
Cc: Ahmad Fatoum <a.fatoum@pengutronix.de>
Cc: Amelie DELAUNAY <amelie.delaunay@foss.st.com>
Cc: Minas Harutyunyan <hminas@synopsys.com>
Cc: Kishon Vijay Abraham I <kishon@ti.com>
Link: https://lore.kernel.org/r/20220407102108.24211-2-jmaselbas@kalray.eu
Signed-off-by: Vinod Koul <vkoul@kernel.org>

drivers/phy/phy-core.c

@@ -229,6 +229,17 @@ void phy_pm_runtime_forbid(struct phy *phy)
 }
 EXPORT_SYMBOL_GPL(phy_pm_runtime_forbid);
 
+/**
+ * phy_init - phy internal initialization before phy operation
+ * @phy: the phy returned by phy_get()
+ *
+ * Used to allow phy's driver to perform phy internal initialization,
+ * such as PLL block powering, clock initialization or anything that's
+ * is required by the phy to perform the start of operation.
+ * Must be called before phy_power_on().
+ *
+ * Return: %0 if successful, a negative error code otherwise
+ */
 int phy_init(struct phy *phy)
 {
 	int ret;
@@ -258,6 +269,14 @@ int phy_init(struct phy *phy)
 }
 EXPORT_SYMBOL_GPL(phy_init);
 
+/**
+ * phy_exit - Phy internal un-initialization
+ * @phy: the phy returned by phy_get()
+ *
+ * Must be called after phy_power_off().
+ *
+ * Return: %0 if successful, a negative error code otherwise
+ */
 int phy_exit(struct phy *phy)
 {
 	int ret;
@@ -287,6 +306,14 @@ int phy_exit(struct phy *phy)
 }
 EXPORT_SYMBOL_GPL(phy_exit);
 
+/**
+ * phy_power_on - Enable the phy and enter proper operation
+ * @phy: the phy returned by phy_get()
+ *
+ * Must be called after phy_init().
+ *
+ * Return: %0 if successful, a negative error code otherwise
+ */
 int phy_power_on(struct phy *phy)
 {
 	int ret = 0;
@@ -329,6 +356,14 @@ int phy_power_on(struct phy *phy)
 }
 EXPORT_SYMBOL_GPL(phy_power_on);
 
+/**
+ * phy_power_off - Disable the phy.
+ * @phy: the phy returned by phy_get()
+ *
+ * Must be called before phy_exit().
+ *
+ * Return: %0 if successful, a negative error code otherwise
+ */
 int phy_power_off(struct phy *phy)
 {
 	int ret;