PM / OPP: Initialize OPP table from device tree

With a lot of devices booting from device tree nowadays, it requires
that OPP table can be initialized from device tree. The patch adds
a helper function of_init_opp_table together with a binding doc for
that purpose.

Signed-off-by: Shawn Guo <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

Documentation/devicetree/bindings/power/opp.txt

···
+* Generic OPP Interface
+
+SoCs have a standard set of tuples consisting of frequency and
+voltage pairs that the device will support per voltage domain. These
+are called Operating Performance Points or OPPs.
+
+Properties:
+- operating-points: An array of 2-tuples items, and each item consists
+  of frequency and voltage like <freq-kHz vol-uV>.
+	freq: clock frequency in kHz
+	vol: voltage in microvolt
+
+Examples:
+
+cpu@0 {
+	compatible = "arm,cortex-a9";
+	reg = <0>;
+	next-level-cache = <&L2>;
+	operating-points = <
+		/* kHz    uV */
+		792000  1100000
+		396000  950000
+		198000  850000
+	>;
+};

drivers/base/power/opp.c

···
 #include <linux/rculist.h>
 #include <linux/rcupdate.h>
 #include <linux/opp.h>
+#include <linux/of.h>
 
 /*
  * Internal data structure organization with the OPP layer library is as
···
 
 	return &dev_opp->head;
 }
+
+#ifdef CONFIG_OF
+/**
+ * of_init_opp_table() - Initialize opp table from device tree
+ * @dev:	device pointer used to lookup device OPPs.
+ *
+ * Register the initial OPP table with the OPP library for given device.
+ */
+int of_init_opp_table(struct device *dev)
+{
+	const struct property *prop;
+	const __be32 *val;
+	int nr;
+
+	prop = of_find_property(dev->of_node, "operating-points", NULL);
+	if (!prop)
+		return -ENODEV;
+	if (!prop->value)
+		return -ENODATA;
+
+	/*
+	 * Each OPP is a set of tuples consisting of frequency and
+	 * voltage like <freq-kHz vol-uV>.
+	 */
+	nr = prop->length / sizeof(u32);
+	if (nr % 2) {
+		dev_err(dev, "%s: Invalid OPP list\n", __func__);
+		return -EINVAL;
+	}
+
+	val = prop->value;
+	while (nr) {
+		unsigned long freq = be32_to_cpup(val++) * 1000;
+		unsigned long volt = be32_to_cpup(val++);
+
+		if (opp_add(dev, freq, volt)) {
+			dev_warn(dev, "%s: Failed to add OPP %ld\n",
+				 __func__, freq);
+			continue;
+		}
+		nr -= 2;
+	}
+
+	return 0;
+}
+#endif

include/linux/opp.h

···
 
 struct srcu_notifier_head *opp_get_notifier(struct device *dev);
 
+#ifdef CONFIG_OF
+int of_init_opp_table(struct device *dev);
+#else
+static inline int of_init_opp_table(struct device *dev)
+{
+	return -EINVAL;
+}
+#endif /* CONFIG_OF */
 #else
 static inline unsigned long opp_get_voltage(struct opp *opp)
 {