struct device_link *device_link_add(struct device *consumer,
				    struct device *supplier, u32 flags)
{
	struct device_link *link;

	if (!consumer || !supplier || flags & ~DL_ADD_VALID_FLAGS ||
	    (flags & DL_FLAG_STATELESS && flags & DL_MANAGED_LINK_FLAGS) ||
	    (flags & DL_FLAG_SYNC_STATE_ONLY &&
	     flags != DL_FLAG_SYNC_STATE_ONLY) ||
	    (flags & DL_FLAG_AUTOPROBE_CONSUMER &&
	     flags & (DL_FLAG_AUTOREMOVE_CONSUMER |
		      DL_FLAG_AUTOREMOVE_SUPPLIER)))
		return NULL;

	if (flags & DL_FLAG_PM_RUNTIME && flags & DL_FLAG_RPM_ACTIVE) {
		if (pm_runtime_get_sync(supplier) < 0) {
			pm_runtime_put_noidle(supplier);
			return NULL;
		}
	}

	if (!(flags & DL_FLAG_STATELESS))
		flags |= DL_FLAG_MANAGED;

	device_links_write_lock();
	device_pm_lock();

	/*
	 * If the supplier has not been fully registered yet or there is a
	 * reverse (non-SYNC_STATE_ONLY) dependency between the consumer and
	 * the supplier already in the graph, return NULL. If the link is a
	 * SYNC_STATE_ONLY link, we don't check for reverse dependencies
	 * because it only affects sync_state() callbacks.
	 */
	if (!device_pm_initialized(supplier)
	    || (!(flags & DL_FLAG_SYNC_STATE_ONLY) &&
		  device_is_dependent(consumer, supplier))) {
		link = NULL;
		goto out;
	}

	/*
	 * DL_FLAG_AUTOREMOVE_SUPPLIER indicates that the link will be needed
	 * longer than for DL_FLAG_AUTOREMOVE_CONSUMER and setting them both
	 * together doesn't make sense, so prefer DL_FLAG_AUTOREMOVE_SUPPLIER.
	 */
	if (flags & DL_FLAG_AUTOREMOVE_SUPPLIER)
		flags &= ~DL_FLAG_AUTOREMOVE_CONSUMER;

	list_for_each_entry(link, &supplier->links.consumers, s_node) {
		if (link->consumer != consumer)
			continue;

		if (flags & DL_FLAG_PM_RUNTIME) {
			if (!(link->flags & DL_FLAG_PM_RUNTIME)) {
				pm_runtime_new_link(consumer);
				link->flags |= DL_FLAG_PM_RUNTIME;
			}
			if (flags & DL_FLAG_RPM_ACTIVE)
				refcount_inc(&link->rpm_active);
		}

		if (flags & DL_FLAG_STATELESS) {
			kref_get(&link->kref);
			if (link->flags & DL_FLAG_SYNC_STATE_ONLY &&
			    !(link->flags & DL_FLAG_STATELESS)) {
				link->flags |= DL_FLAG_STATELESS;
				goto reorder;
			} else {
				link->flags |= DL_FLAG_STATELESS;
				goto out;
			}
		}

		/*
		 * If the life time of the link following from the new flags is
		 * longer than indicated by the flags of the existing link,
		 * update the existing link to stay around longer.
		 */
		if (flags & DL_FLAG_AUTOREMOVE_SUPPLIER) {
			if (link->flags & DL_FLAG_AUTOREMOVE_CONSUMER) {
				link->flags &= ~DL_FLAG_AUTOREMOVE_CONSUMER;
				link->flags |= DL_FLAG_AUTOREMOVE_SUPPLIER;
			}
		} else if (!(flags & DL_FLAG_AUTOREMOVE_CONSUMER)) {
			link->flags &= ~(DL_FLAG_AUTOREMOVE_CONSUMER |
					 DL_FLAG_AUTOREMOVE_SUPPLIER);
		}
		if (!(link->flags & DL_FLAG_MANAGED)) {
			kref_get(&link->kref);
			link->flags |= DL_FLAG_MANAGED;
			device_link_init_status(link, consumer, supplier);
		}
		if (link->flags & DL_FLAG_SYNC_STATE_ONLY &&
		    !(flags & DL_FLAG_SYNC_STATE_ONLY)) {
			link->flags &= ~DL_FLAG_SYNC_STATE_ONLY;
			goto reorder;
		}

		goto out;
	}

	link = kzalloc(sizeof(*link), GFP_KERNEL);
	if (!link)
		goto out;

	refcount_set(&link->rpm_active, 1);

	get_device(supplier);
	link->supplier = supplier;
	INIT_LIST_HEAD(&link->s_node);
	get_device(consumer);
	link->consumer = consumer;
	INIT_LIST_HEAD(&link->c_node);
	link->flags = flags;
	kref_init(&link->kref);

	link->link_dev.class = &devlink_class;
	device_set_pm_not_required(&link->link_dev);
	dev_set_name(&link->link_dev, "%s--%s",
		     dev_name(supplier), dev_name(consumer));
	if (device_register(&link->link_dev)) {
		put_device(consumer);
		put_device(supplier);
		kfree(link);
		link = NULL;
		goto out;
	}

	if (flags & DL_FLAG_PM_RUNTIME) {
		if (flags & DL_FLAG_RPM_ACTIVE)
			refcount_inc(&link->rpm_active);

		pm_runtime_new_link(consumer);
	}

	/* Determine the initial link state. */
	if (flags & DL_FLAG_STATELESS)
		link->status = DL_STATE_NONE;
	else
		device_link_init_status(link, consumer, supplier);

	/*
	 * Some callers expect the link creation during consumer driver probe to
	 * resume the supplier even without DL_FLAG_RPM_ACTIVE.
	 */
	if (link->status == DL_STATE_CONSUMER_PROBE &&
	    flags & DL_FLAG_PM_RUNTIME)
		pm_runtime_resume(supplier);

	list_add_tail_rcu(&link->s_node, &supplier->links.consumers);
	list_add_tail_rcu(&link->c_node, &consumer->links.suppliers);

	if (flags & DL_FLAG_SYNC_STATE_ONLY) {
		dev_dbg(consumer,
			"Linked as a sync state only consumer to %s\n",
			dev_name(supplier));
		goto out;
	}

reorder:
	/*
	 * Move the consumer and all of the devices depending on it to the end
	 * of dpm_list and the devices_kset list.
	 *
	 * It is necessary to hold dpm_list locked throughout all that or else
	 * we may end up suspending with a wrong ordering of it.
	 */
	device_reorder_to_tail(consumer, NULL);

	dev_dbg(consumer, "Linked as a consumer to %s\n", dev_name(supplier));

out:
	device_pm_unlock();
	device_links_write_unlock();

	if ((flags & DL_FLAG_PM_RUNTIME && flags & DL_FLAG_RPM_ACTIVE) && !link)
		pm_runtime_put(supplier);

	return link;
}