Index: head/sys/kern/subr_bus.c
===================================================================
--- head/sys/kern/subr_bus.c
+++ head/sys/kern/subr_bus.c
@@ -3708,7 +3708,11 @@
 	if (dev->state != DS_ATTACHED)
 		return (EBUSY);
 
-	TAILQ_FOREACH(child, &dev->children, link) {
+	/*
+	 * Detach children in the reverse order.
+	 * See bus_generic_suspend for details.
+	 */
+	TAILQ_FOREACH_REVERSE(child, &dev->children, device_list, link) {
 		if ((error = device_detach(child)) != 0)
 			return (error);
 	}
@@ -3728,7 +3732,11 @@
 {
 	device_t child;
 
-	TAILQ_FOREACH(child, &dev->children, link) {
+	/*
+	 * Shut down children in the reverse order.
+	 * See bus_generic_suspend for details.
+	 */
+	TAILQ_FOREACH_REVERSE(child, &dev->children, device_list, link) {
 		device_shutdown(child);
 	}
 
@@ -3781,15 +3789,23 @@
 bus_generic_suspend(device_t dev)
 {
 	int		error;
-	device_t	child, child2;
+	device_t	child;
 
-	TAILQ_FOREACH(child, &dev->children, link) {
+	/*
+	 * Suspend children in the reverse order.
+	 * For most buses all children are equal, so the order does not matter.
+	 * Other buses, such as acpi, carefully order their child devices to
+	 * express implicit dependencies between them.  For such buses it is
+	 * safer to bring down devices in the reverse order.
+	 */
+	TAILQ_FOREACH_REVERSE(child, &dev->children, device_list, link) {
 		error = BUS_SUSPEND_CHILD(dev, child);
-		if (error) {
-			for (child2 = TAILQ_FIRST(&dev->children);
-			     child2 && child2 != child;
-			     child2 = TAILQ_NEXT(child2, link))
-				BUS_RESUME_CHILD(dev, child2);
+		if (error != 0) {
+			child = TAILQ_NEXT(child, link);
+			if (child != NULL) {
+				TAILQ_FOREACH_FROM(child, &dev->children, link)
+					BUS_RESUME_CHILD(dev, child);
+			}
 			return (error);
 		}
 	}