device/device_util: Add function to determine bridge state

Add a method to get the state of a bridge device.
Return true if at least one enabled device on the secondary
bus is found.

Useful to disable non hotplugable bridges without any devices attached.

Change-Id: Ic8fe539d233031d4d177b03dd2c03edb5ab8c88d
Signed-off-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-on: https://review.coreboot.org/19817
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Philippe Mathieu-Daudé <philippe.mathieu.daude@gmail.com>
Reviewed-by: Martin Roth <martinroth@google.com>

src/device/device_util.c

@@ -775,6 +775,31 @@ void disable_children(struct bus *bus)
 	}
 }
 
+/*
+ * Returns true if the device is an enabled bridge that has at least
+ * one enabled device on its secondary bus.
+ */
+bool dev_is_active_bridge(device_t dev)
+{
+	struct bus *link;
+	device_t child;
+
+	if (!dev || !dev->enabled)
+		return 0;
+
+	if (!dev->link_list || !dev->link_list->children)
+		return 0;
+
+	for (link = dev->link_list; link; link = link->next) {
+		for (child = link->children; child; child = child->sibling) {
+			if (child->enabled)
+				return 1;
+		}
+	}
+
+	return 0;
+}
+
 static void resource_tree(struct device *root, int debug_level, int depth)
 {
 	int i = 0;

src/include/device/device.h

@@ -190,6 +190,7 @@ u32 dev_path_encode(device_t dev);
 const char *bus_path(struct bus *bus);
 void dev_set_enabled(device_t dev, int enable);
 void disable_children(struct bus *bus);
+bool dev_is_active_bridge(device_t dev);
 
 /* Option ROM helper functions */
 void run_bios(struct device *dev, unsigned long addr);