media: v4l: fwnode: Add a helper function for parsing generic references

Add function v4l2_fwnode_reference_parse() for parsing them as async
sub-devices. This can be done on e.g. flash or lens async sub-devices that
are not part of but are associated with a sensor.
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/v4l2-core/v4l2-fwnode.c

@@ -509,6 +509,75 @@ int v4l2_async_notifier_parse_fwnode_endpoints_by_port(
 }
 EXPORT_SYMBOL_GPL(v4l2_async_notifier_parse_fwnode_endpoints_by_port);
 
+/*
+ * v4l2_fwnode_reference_parse - parse references for async sub-devices
+ * @dev: the device node the properties of which are parsed for references
+ * @notifier: the async notifier where the async subdevs will be added
+ * @prop: the name of the property
+ *
+ * Return: 0 on success
+ *	   -ENOENT if no entries were found
+ *	   -ENOMEM if memory allocation failed
+ *	   -EINVAL if property parsing failed
+ */
+static int v4l2_fwnode_reference_parse(
+	struct device *dev, struct v4l2_async_notifier *notifier,
+	const char *prop)
+{
+	struct fwnode_reference_args args;
+	unsigned int index;
+	int ret;
+
+	for (index = 0;
+	     !(ret = fwnode_property_get_reference_args(
+		       dev_fwnode(dev), prop, NULL, 0, index, &args));
+	     index++)
+		fwnode_handle_put(args.fwnode);
+
+	if (!index)
+		return -ENOENT;
+
+	/*
+	 * Note that right now both -ENODATA and -ENOENT may signal
+	 * out-of-bounds access. Return the error in cases other than that.
+	 */
+	if (ret != -ENOENT && ret != -ENODATA)
+		return ret;
+
+	ret = v4l2_async_notifier_realloc(notifier,
+					  notifier->num_subdevs + index);
+	if (ret)
+		return ret;
+
+	for (index = 0; !fwnode_property_get_reference_args(
+		     dev_fwnode(dev), prop, NULL, 0, index, &args);
+	     index++) {
+		struct v4l2_async_subdev *asd;
+
+		if (WARN_ON(notifier->num_subdevs >= notifier->max_subdevs)) {
+			ret = -EINVAL;
+			goto error;
+		}
+
+		asd = kzalloc(sizeof(*asd), GFP_KERNEL);
+		if (!asd) {
+			ret = -ENOMEM;
+			goto error;
+		}
+
+		notifier->subdevs[notifier->num_subdevs] = asd;
+		asd->match.fwnode.fwnode = args.fwnode;
+		asd->match_type = V4L2_ASYNC_MATCH_FWNODE;
+		notifier->num_subdevs++;
+	}
+
+	return 0;
+
+error:
+	fwnode_handle_put(args.fwnode);
+	return ret;
+}
+
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Sakari Ailus <sakari.ailus@linux.intel.com>");
 MODULE_AUTHOR("Sylwester Nawrocki <s.nawrocki@samsung.com>");