reset: Add reset_control_get_count()

Currently the reset core has internal support for counting the number of
resets for a device described in DT.  Generalize this to devices using
lookup resets, and export it for public use.

This will be used by generic drivers that need to be sure a device is
controlled by a single, dedicated reset line (e.g. vfio-platform).

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
[p.zabel@pengutronix.de: fixed a typo in reset_control_get_count comment]
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

drivers/reset/core.c

@@ -795,3 +795,44 @@ devm_reset_control_array_get(struct device *dev, bool shared, bool optional)
 	return rstc;
 }
 EXPORT_SYMBOL_GPL(devm_reset_control_array_get);
+
+static int reset_control_get_count_from_lookup(struct device *dev)
+{
+	const struct reset_control_lookup *lookup;
+	const char *dev_id = dev_name(dev);
+	int count = 0;
+
+	if (!dev)
+		return -EINVAL;
+
+	mutex_lock(&reset_lookup_mutex);
+
+	list_for_each_entry(lookup, &reset_lookup_list, list) {
+		if (!strcmp(lookup->dev_id, dev_id))
+			count++;
+	}
+
+	mutex_unlock(&reset_lookup_mutex);
+
+	if (count == 0)
+		count = -ENOENT;
+
+	return count;
+}
+
+/**
+ * reset_control_get_count - Count number of resets available with a device
+ *
+ * @dev: device for which to return the number of resets
+ *
+ * Returns positive reset count on success, or error number on failure and
+ * on count being zero.
+ */
+int reset_control_get_count(struct device *dev)
+{
+	if (dev->of_node)
+		return of_reset_control_get_count(dev->of_node);
+
+	return reset_control_get_count_from_lookup(dev);
+}
+EXPORT_SYMBOL_GPL(reset_control_get_count);

include/linux/reset.h

@@ -32,6 +32,8 @@ struct reset_control *devm_reset_control_array_get(struct device *dev,
 struct reset_control *of_reset_control_array_get(struct device_node *np,
 						 bool shared, bool optional);
 
+int reset_control_get_count(struct device *dev);
+
 #else
 
 static inline int reset_control_reset(struct reset_control *rstc)
@@ -97,6 +99,11 @@ of_reset_control_array_get(struct device_node *np, bool shared, bool optional)
 	return optional ? NULL : ERR_PTR(-ENOTSUPP);
 }
 
+static inline int reset_control_get_count(struct device *dev)
+{
+	return -ENOENT;
+}
+
 #endif /* CONFIG_RESET_CONTROLLER */
 
 static inline int __must_check device_reset(struct device *dev)