clk: Introduce optional unprepare_unused callback

An unprepare_unused callback is introduced due to the same reasons to
why the disable_unused callback was added.

During the clk_disable_unused sequence, those clk_hw that needs specific
treatment with regards to being unprepared, shall implement the
unprepare_unused callback.

Signed-off-by: Ulf Hansson <[e-mail]>
Acked-by: Linus Walleij <[e-mail]>
Signed-off-by: Mike Turquette <[e-mail]>

drivers/clk/clk.c

···
 	if (clk->flags & CLK_IGNORE_UNUSED)
 		return;
 
-	if (__clk_is_prepared(clk))
-		if (clk->ops->unprepare)
+	if (__clk_is_prepared(clk)) {
+		if (clk->ops->unprepare_unused)
+			clk->ops->unprepare_unused(clk->hw);
+		else if (clk->ops->unprepare)
 			clk->ops->unprepare(clk->hw);
+	}
 }
 
 /* caller must hold prepare_lock */

include/linux/clk-provider.h

···
  *		This function is allowed to sleep. Optional, if this op is not
  *		set then the prepare count will be used.
  *
+ * @unprepare_unused: Unprepare the clock atomically.  Only called from
+ *		clk_disable_unused for prepare clocks with special needs.
+ *		Called with prepare mutex held. This function may sleep.
+ *
  * @enable:	Enable the clock atomically. This must not return until the
  * 		clock is generating a valid clock signal, usable by consumer
  * 		devices. Called with enable_lock held. This function must not
···
 	int		(*prepare)(struct clk_hw *hw);
 	void		(*unprepare)(struct clk_hw *hw);
 	int		(*is_prepared)(struct clk_hw *hw);
+	void		(*unprepare_unused)(struct clk_hw *hw);
 	int		(*enable)(struct clk_hw *hw);
 	void		(*disable)(struct clk_hw *hw);
 	int		(*is_enabled)(struct clk_hw *hw);