clk: Add __clk_mux_determine_rate_closest

Some clock drivers want to find the closest rate on the input of
a mux instead of a rate that's less than or equal to the desired
rate. Add a generic mux function to support this.
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Tested-by: Kenneth Westfield <kwestfie@codeaurora.org>
Signed-off-by: Michael Turquette <mturquette@linaro.org>

drivers/clk/clk.c

@@ -690,14 +690,20 @@ struct clk *__clk_lookup(const char *name)
 	return NULL;
 }
 
-/*
- * Helper for finding best parent to provide a given frequency. This can be used
- * directly as a determine_rate callback (e.g. for a mux), or from a more
- * complex clock that may combine a mux with other operations.
- */
-long __clk_mux_determine_rate(struct clk_hw *hw, unsigned long rate,
+static bool mux_is_better_rate(unsigned long rate, unsigned long now,
+			   unsigned long best, unsigned long flags)
+{
+	if (flags & CLK_MUX_ROUND_CLOSEST)
+		return abs(now - rate) < abs(best - rate);
+
+	return now <= rate && now > best;
+}
+
+static long
+clk_mux_determine_rate_flags(struct clk_hw *hw, unsigned long rate,
 			     unsigned long *best_parent_rate,
-			      struct clk_hw **best_parent_p)
+			     struct clk_hw **best_parent_p,
+			     unsigned long flags)
 {
 	struct clk *clk = hw->clk, *parent, *best_parent = NULL;
 	int i, num_parents;
@@ -725,7 +731,7 @@ long __clk_mux_determine_rate(struct clk_hw *hw, unsigned long rate,
 			parent_rate = __clk_round_rate(parent, rate);
 		else
 			parent_rate = __clk_get_rate(parent);
-		if (parent_rate <= rate && parent_rate > best) {
+		if (mux_is_better_rate(rate, parent_rate, best, flags)) {
 			best_parent = parent;
 			best = parent_rate;
 		}
@@ -738,8 +744,31 @@ long __clk_mux_determine_rate(struct clk_hw *hw, unsigned long rate,
 
 	return best;
 }
+
+/*
+ * Helper for finding best parent to provide a given frequency. This can be used
+ * directly as a determine_rate callback (e.g. for a mux), or from a more
+ * complex clock that may combine a mux with other operations.
+ */
+long __clk_mux_determine_rate(struct clk_hw *hw, unsigned long rate,
+			      unsigned long *best_parent_rate,
+			      struct clk_hw **best_parent_p)
+{
+	return clk_mux_determine_rate_flags(hw, rate, best_parent_rate,
+					    best_parent_p, 0);
+}
 EXPORT_SYMBOL_GPL(__clk_mux_determine_rate);
 
+long __clk_mux_determine_rate_closest(struct clk_hw *hw, unsigned long rate,
+			      unsigned long *best_parent_rate,
+			      struct clk_hw **best_parent_p)
+{
+	return clk_mux_determine_rate_flags(hw, rate, best_parent_rate,
+					    best_parent_p,
+					    CLK_MUX_ROUND_CLOSEST);
+}
+EXPORT_SYMBOL_GPL(__clk_mux_determine_rate_closest);
+
 /***        clk api        ***/
 
 void __clk_unprepare(struct clk *clk)

include/linux/clk-provider.h

@@ -384,6 +384,8 @@ void clk_unregister_divider(struct clk *clk);
  *	register, and mask of mux bits are in higher 16-bit of this register.
  *	While setting the mux bits, higher 16-bit should also be updated to
  *	indicate changing mux bits.
+ * CLK_MUX_ROUND_CLOSEST - Use the parent rate that is closest to the desired
+ *	frequency.
  */
 struct clk_mux {
 	struct clk_hw	hw;
@@ -398,7 +400,8 @@ struct clk_mux {
 #define CLK_MUX_INDEX_ONE		BIT(0)
 #define CLK_MUX_INDEX_BIT		BIT(1)
 #define CLK_MUX_HIWORD_MASK		BIT(2)
-#define CLK_MUX_READ_ONLY	BIT(3) /* mux setting cannot be changed */
+#define CLK_MUX_READ_ONLY		BIT(3) /* mux can't be changed */
+#define CLK_MUX_ROUND_CLOSEST		BIT(4)
 
 extern const struct clk_ops clk_mux_ops;
 extern const struct clk_ops clk_mux_ro_ops;
@@ -556,6 +559,9 @@ struct clk *__clk_lookup(const char *name);
 long __clk_mux_determine_rate(struct clk_hw *hw, unsigned long rate,
 			      unsigned long *best_parent_rate,
 			      struct clk_hw **best_parent_p);
+long __clk_mux_determine_rate_closest(struct clk_hw *hw, unsigned long rate,
+			      unsigned long *best_parent_rate,
+			      struct clk_hw **best_parent_p);
 
 /*
  * FIXME clock api without lock protection