drivers property: When no children in primary, try secondary

Software firmware nodes can provide a child node to its parent.
Since software node can be secondary, we need a mechanism to access
the children. The idea is to list children of the primary node first
and when they are finished, continue with secondary node if available.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20200520102959.34812-1-andriy.shevchenko@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/base/property.c

@@ -708,14 +708,23 @@ struct fwnode_handle *device_get_next_child_node(struct device *dev,
 						 struct fwnode_handle *child)
 {
 	struct acpi_device *adev = ACPI_COMPANION(dev);
-	struct fwnode_handle *fwnode = NULL;
+	struct fwnode_handle *fwnode = NULL, *next;
 
 	if (dev->of_node)
 		fwnode = &dev->of_node->fwnode;
 	else if (adev)
 		fwnode = acpi_fwnode_handle(adev);
 
-	return fwnode_get_next_child_node(fwnode, child);
+	/* Try to find a child in primary fwnode */
+	next = fwnode_get_next_child_node(fwnode, child);
+	if (next)
+		return next;
+
+	/* When no more children in primary, continue with secondary */
+	if (!IS_ERR_OR_NULL(fwnode->secondary))
+		next = fwnode_get_next_child_node(fwnode->secondary, child);
+
+	return next;
 }
 EXPORT_SYMBOL_GPL(device_get_next_child_node);