clk: Add API to get index of the clock parent

This patch adds a new clk_hw_get_parent_index() function that can be
used to retrieve the index of a given clock's parent. This can be useful
for restoring a clock on system resume.

Reviewed-by: Thierry Reding <treding@nvidia.com>
Reviewed-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Sowjanya Komatineni <skomatineni@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/clk/clk.c

@@ -1674,6 +1674,24 @@ static int clk_fetch_parent_index(struct clk_core *core,
 	return i;
 }
 
+/**
+ * clk_hw_get_parent_index - return the index of the parent clock
+ * @hw: clk_hw associated with the clk being consumed
+ *
+ * Fetches and returns the index of parent clock. Returns -EINVAL if the given
+ * clock does not have a current parent.
+ */
+int clk_hw_get_parent_index(struct clk_hw *hw)
+{
+	struct clk_hw *parent = clk_hw_get_parent(hw);
+
+	if (WARN_ON(parent == NULL))
+		return -EINVAL;
+
+	return clk_fetch_parent_index(hw->core, parent->core);
+}
+EXPORT_SYMBOL_GPL(clk_hw_get_parent_index);
+
 /*
  * Update the orphan status of @core and all its children.
  */

include/linux/clk-provider.h

@@ -818,6 +818,7 @@ unsigned int clk_hw_get_num_parents(const struct clk_hw *hw);
 struct clk_hw *clk_hw_get_parent(const struct clk_hw *hw);
 struct clk_hw *clk_hw_get_parent_by_index(const struct clk_hw *hw,
 					  unsigned int index);
+int clk_hw_get_parent_index(struct clk_hw *hw);
 int clk_hw_set_parent(struct clk_hw *hw, struct clk_hw *new_parent);
 unsigned int __clk_get_enable_count(struct clk *clk);
 unsigned long clk_hw_get_rate(const struct clk_hw *hw);