clk: add clock-indices support

Add a property called clock-indices to allow clock-output-names
to be used where the index used to lookup a clock is not a 1:1
mapping to the array position in the clock-output-names

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Mike Turquette <mturquette@linaro.org>

Documentation/devicetree/bindings/clock/clock-bindings.txt

@@ -44,6 +44,23 @@ For example:
   clocks by index. The names should reflect the clock output signal
   names for the device.
 
+clock-indices:	   If the identifyng number for the clocks in the node
+		   is not linear from zero, then the this mapping allows
+		   the mapping of identifiers into the clock-output-names
+		   array.
+
+For example, if we have two clocks <&oscillator 1> and <&oscillator 3>:
+
+	oscillator {
+		compatible = "myclocktype";
+		#clock-cells = <1>;
+		clock-indices = <1>, <3>;
+		clock-output-names = "clka", "clkb";
+	}
+
+	This ensures we do not have any empty nodes in clock-output-names
+
+
 ==Clock consumers==
 
 Required properties:

drivers/clk/clk.c

@@ -2496,8 +2496,12 @@ EXPORT_SYMBOL_GPL(of_clk_get_parent_count);
 const char *of_clk_get_parent_name(struct device_node *np, int index)
 {
 	struct of_phandle_args clkspec;
+	struct property *prop;
 	const char *clk_name;
+	const __be32 *vp;
+	u32 pv;
 	int rc;
+	int count;
 
 	if (index < 0)
 		return NULL;
@@ -2507,8 +2511,22 @@ const char *of_clk_get_parent_name(struct device_node *np, int index)
 	if (rc)
 		return NULL;
 
+	index = clkspec.args_count ? clkspec.args[0] : 0;
+	count = 0;
+
+	/* if there is an indices property, use it to transfer the index
+	 * specified into an array offset for the clock-output-names property.
+	 */
+	of_property_for_each_u32(clkspec.np, "clock-indices", prop, vp, pv) {
+		if (index == pv) {
+			index = count;
+			break;
+		}
+		count++;
+	}
+
 	if (of_property_read_string_index(clkspec.np, "clock-output-names",
-					  clkspec.args_count ? clkspec.args[0] : 0,
+					  index,
 					  &clk_name) < 0)
 		clk_name = clkspec.np->name;