dm: clk: Add support for decoding clocks from the device tree

Add a method which can locate a clock for a device, given its index. This
uses the normal device tree bindings to return the clock device and the
first argument which is normally used as a peripheral ID in U-Boot.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Masahiro Yamada <yamada.masahiro@socionext.com>

drivers/clk/clk-uclass.c

@@ -12,6 +12,8 @@
 #include <dm/lists.h>
 #include <dm/root.h>
 
+DECLARE_GLOBAL_DATA_PTR;
+
 ulong clk_get_rate(struct udevice *dev)
 {
 	struct clk_ops *ops = clk_get_ops(dev);
@@ -62,6 +64,32 @@ ulong clk_set_periph_rate(struct udevice *dev, int periph, ulong rate)
 	return ops->set_periph_rate(dev, periph, rate);
 }
 
+#if CONFIG_IS_ENABLED(OF_CONTROL)
+int clk_get_by_index(struct udevice *dev, int index, struct udevice **clk_devp)
+{
+	struct fdtdec_phandle_args args;
+	int ret;
+
+	assert(*clk_devp);
+	ret = fdtdec_parse_phandle_with_args(gd->fdt_blob, dev->of_offset,
+					     "clocks", "#clock-cells", 0, index,
+					     &args);
+	if (ret) {
+		debug("%s: fdtdec_parse_phandle_with_args failed: err=%d\n",
+		      __func__, ret);
+		return ret;
+	}
+
+	ret = uclass_get_device_by_of_offset(UCLASS_CLK, args.node, clk_devp);
+	if (ret) {
+		debug("%s: uclass_get_device_by_of_offset failed: err=%d\n",
+		      __func__, ret);
+		return ret;
+	}
+	return args.args_count > 0 ? args.args[0] : 0;
+}
+#endif
+
 UCLASS_DRIVER(clk) = {
 	.id		= UCLASS_CLK,
 	.name		= "clk",

include/clk.h

@@ -8,6 +8,7 @@
 #ifndef _CLK_H_
 #define _CLK_H_
 
+#include <errno.h>
 #include <linux/types.h>
 
 struct udevice;
@@ -105,4 +106,27 @@ ulong clk_get_periph_rate(struct udevice *dev, int periph);
  */
 ulong clk_set_periph_rate(struct udevice *dev, int periph, ulong rate);
 
+#if CONFIG_IS_ENABLED(OF_CONTROL)
+/**
+ * clk_get_by_index() - look up a clock referenced by a device
+ *
+ * Parse a device's 'clocks' list, returning information on the indexed clock,
+ * ensuring that it is activated.
+ *
+ * @dev:	Device containing the clock reference
+ * @index:	Clock index to return (0 = first)
+ * @clk_devp:	Returns clock device
+ * @return:	Peripheral ID for the device to control. This is the first
+ *		argument after the clock node phandle. If there is no arguemnt,
+ *		returns 0. Return -ve error code on any error
+ */
+int clk_get_by_index(struct udevice *dev, int index, struct udevice **clk_devp);
+#else
+static inline int clk_get_by_index(struct udevice *dev, int index,
+				   struct udevice **clk_devp)
+{
+	return -ENOSYS;
+}
+#endif
+
 #endif /* _CLK_H_ */