drivers/media/media-entity.c

/*
 * Media entity
 *
 * Copyright (C) 2010 Nokia Corporation
 *
 * Contacts: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
 *	     Sakari Ailus <sakari.ailus@iki.fi>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include <linux/bitmap.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <media/media-entity.h>
#include <media/media-device.h>

/**
 *  dev_dbg_obj - Prints in debug mode a change on some object
 *
 * @event_name:	Name of the event to report. Could be __func__
 * @gobj:	Pointer to the object
 *
 * Enabled only if DEBUG or CONFIG_DYNAMIC_DEBUG. Otherwise, it
 * won't produce any code.
 */
static inline const char *gobj_type(enum media_gobj_type type)
{
	switch (type) {
	case MEDIA_GRAPH_ENTITY:
		return "entity";
	case MEDIA_GRAPH_PAD:
		return "pad";
	case MEDIA_GRAPH_LINK:
		return "link";
	case MEDIA_GRAPH_INTF_DEVNODE:
		return "intf-devnode";
	default:
		return "unknown";
	}
}

static inline const char *intf_type(struct media_interface *intf)
{
	switch (intf->type) {
	case MEDIA_INTF_T_DVB_FE:
		return "frontend";
	case MEDIA_INTF_T_DVB_DEMUX:
		return "demux";
	case MEDIA_INTF_T_DVB_DVR:
		return "DVR";
	case MEDIA_INTF_T_DVB_CA:
		return  "CA";
	case MEDIA_INTF_T_DVB_NET:
		return "dvbnet";
	case MEDIA_INTF_T_V4L_VIDEO:
		return "video";
	case MEDIA_INTF_T_V4L_VBI:
		return "vbi";
	case MEDIA_INTF_T_V4L_RADIO:
		return "radio";
	case MEDIA_INTF_T_V4L_SUBDEV:
		return "v4l2-subdev";
	case MEDIA_INTF_T_V4L_SWRADIO:
		return "swradio";
	default:
		return "unknown-intf";
	}
};

static void dev_dbg_obj(const char *event_name,  struct media_gobj *gobj)
{
#if defined(DEBUG) || defined (CONFIG_DYNAMIC_DEBUG)
	switch (media_type(gobj)) {
	case MEDIA_GRAPH_ENTITY:
		dev_dbg(gobj->mdev->dev,
			"%s: id 0x%08x entity#%d: '%s'\n",
			event_name, gobj->id, media_localid(gobj),
			gobj_to_entity(gobj)->name);
		break;
	case MEDIA_GRAPH_LINK:
	{
		struct media_link *link = gobj_to_link(gobj);

		dev_dbg(gobj->mdev->dev,
			"%s: id 0x%08x link#%d: %s#%d ==> %s#%d\n",
			event_name, gobj->id, media_localid(gobj),

			gobj_type(media_type(link->gobj0)),
			media_localid(link->gobj0),

			gobj_type(media_type(link->gobj1)),
			media_localid(link->gobj1));
		break;
	}
	case MEDIA_GRAPH_PAD:
	{
		struct media_pad *pad = gobj_to_pad(gobj);

		dev_dbg(gobj->mdev->dev,
			"%s: id 0x%08x %s%spad#%d: '%s':%d\n",
			event_name, gobj->id,
			pad->flags & MEDIA_PAD_FL_SINK   ? "  sink " : "",
			pad->flags & MEDIA_PAD_FL_SOURCE ? "source " : "",
			media_localid(gobj),
			pad->entity->name, pad->index);
		break;
	}
	case MEDIA_GRAPH_INTF_DEVNODE:
	{
		struct media_interface *intf = gobj_to_intf(gobj);
		struct media_intf_devnode *devnode = intf_to_devnode(intf);

		dev_dbg(gobj->mdev->dev,
			"%s: id 0x%08x intf_devnode#%d: %s - major: %d, minor: %d\n",
			event_name, gobj->id, media_localid(gobj),
			intf_type(intf),
			devnode->major, devnode->minor);
		break;
	}
	}
#endif
}

/**
 *  media_gobj_init - Initialize a graph object
 *
 * @mdev:	Pointer to the media_device that contains the object
 * @type:	Type of the object
 * @gobj:	Pointer to the object
 *
 * This routine initializes the embedded struct media_gobj inside a
 * media graph object. It is called automatically if media_*_create()
 * calls are used. However, if the object (entity, link, pad, interface)
 * is embedded on some other object, this function should be called before
 * registering the object at the media controller.
 */
void media_gobj_init(struct media_device *mdev,
			   enum media_gobj_type type,
			   struct media_gobj *gobj)
{
	BUG_ON(!mdev);

	gobj->mdev = mdev;

	/* Create a per-type unique object ID */
	switch (type) {
	case MEDIA_GRAPH_ENTITY:
		gobj->id = media_gobj_gen_id(type, ++mdev->entity_id);
		list_add_tail(&gobj->list, &mdev->entities);
		break;
	case MEDIA_GRAPH_PAD:
		gobj->id = media_gobj_gen_id(type, ++mdev->pad_id);
		break;
	case MEDIA_GRAPH_LINK:
		gobj->id = media_gobj_gen_id(type, ++mdev->link_id);
		break;
	case MEDIA_GRAPH_INTF_DEVNODE:
		list_add_tail(&gobj->list, &mdev->interfaces);
		gobj->id = media_gobj_gen_id(type, ++mdev->intf_devnode_id);
		break;
	}
	dev_dbg_obj(__func__, gobj);
}

/**
 *  media_gobj_remove - Stop using a graph object on a media device
 *
 * @graph_obj:	Pointer to the object
 *
 * This should be called at media_device_unregister_*() routines
 */
void media_gobj_remove(struct media_gobj *gobj)
{
	/* Remove the object from mdev list */
	switch (media_type(gobj)) {
	case MEDIA_GRAPH_ENTITY:
	case MEDIA_GRAPH_INTF_DEVNODE:
		list_del(&gobj->list);
		break;
	default:
		break;
	}

	dev_dbg_obj(__func__, gobj);
}

/**
 * media_entity_init - Initialize a media entity
 *
 * @num_pads: Total number of sink and source pads.
 * @pads: Array of 'num_pads' pads.
 *
 * The total number of pads is an intrinsic property of entities known by the
 * entity driver, while the total number of links depends on hardware design
 * and is an extrinsic property unknown to the entity driver. However, in most
 * use cases the number of links can safely be assumed to be equal to or
 * larger than the number of pads.
 *
 * For those reasons the links array can be preallocated based on the number
 * of pads and will be reallocated later if extra links need to be created.
 *
 * This function allocates a links array with enough space to hold at least
 * 'num_pads' elements. The media_entity::max_links field will be set to the
 * number of allocated elements.
 *
 * The pads array is managed by the entity driver and passed to
 * media_entity_init() where its pointer will be stored in the entity structure.
 */
int
media_entity_init(struct media_entity *entity, u16 num_pads,
		  struct media_pad *pads)
{
	unsigned int i;

	entity->group_id = 0;
	entity->num_links = 0;
	entity->num_backlinks = 0;
	entity->num_pads = num_pads;
	entity->pads = pads;

	for (i = 0; i < num_pads; i++) {
		pads[i].entity = entity;
		pads[i].index = i;
	}

	return 0;
}
EXPORT_SYMBOL_GPL(media_entity_init);

void
media_entity_cleanup(struct media_entity *entity)
{
	struct media_link *link, *tmp;

	list_for_each_entry_safe(link, tmp, &entity->links, list) {
		media_gobj_remove(&link->graph_obj);
		list_del(&link->list);
		kfree(link);
	}
}
EXPORT_SYMBOL_GPL(media_entity_cleanup);

/* -----------------------------------------------------------------------------
 * Graph traversal
 */

static struct media_entity *
media_entity_other(struct media_entity *entity, struct media_link *link)
{
	if (link->source->entity == entity)
		return link->sink->entity;
	else
		return link->source->entity;
}

/* push an entity to traversal stack */
static void stack_push(struct media_entity_graph *graph,
		       struct media_entity *entity)
{
	if (graph->top == MEDIA_ENTITY_ENUM_MAX_DEPTH - 1) {
		WARN_ON(1);
		return;
	}
	graph->top++;
	graph->stack[graph->top].link = (&entity->links)->next;
	graph->stack[graph->top].entity = entity;
}

static struct media_entity *stack_pop(struct media_entity_graph *graph)
{
	struct media_entity *entity;

	entity = graph->stack[graph->top].entity;
	graph->top--;

	return entity;
}

#define link_top(en)	((en)->stack[(en)->top].link)
#define stack_top(en)	((en)->stack[(en)->top].entity)

/**
 * media_entity_graph_walk_start - Start walking the media graph at a given entity
 * @graph: Media graph structure that will be used to walk the graph
 * @entity: Starting entity
 *
 * This function initializes the graph traversal structure to walk the entities
 * graph starting at the given entity. The traversal structure must not be
 * modified by the caller during graph traversal. When done the structure can
 * safely be freed.
 */
void media_entity_graph_walk_start(struct media_entity_graph *graph,
				   struct media_entity *entity)
{
	graph->top = 0;
	graph->stack[graph->top].entity = NULL;
	bitmap_zero(graph->entities, MEDIA_ENTITY_ENUM_MAX_ID);

	if (WARN_ON(media_entity_id(entity) >= MEDIA_ENTITY_ENUM_MAX_ID))
		return;

	__set_bit(media_entity_id(entity), graph->entities);
	stack_push(graph, entity);
}
EXPORT_SYMBOL_GPL(media_entity_graph_walk_start);


/**
 * media_entity_graph_walk_next - Get the next entity in the graph
 * @graph: Media graph structure
 *
 * Perform a depth-first traversal of the given media entities graph.
 *
 * The graph structure must have been previously initialized with a call to
 * media_entity_graph_walk_start().
 *
 * Return the next entity in the graph or NULL if the whole graph have been
 * traversed.
 */
struct media_entity *
media_entity_graph_walk_next(struct media_entity_graph *graph)
{
	if (stack_top(graph) == NULL)
		return NULL;

	/*
	 * Depth first search. Push entity to stack and continue from
	 * top of the stack until no more entities on the level can be
	 * found.
	 */
	while (link_top(graph) != &(stack_top(graph)->links)) {
		struct media_entity *entity = stack_top(graph);
		struct media_link *link;
		struct media_entity *next;

		link = list_entry(link_top(graph), typeof(*link), list);

		/* The link is not enabled so we do not follow. */
		if (!(link->flags & MEDIA_LNK_FL_ENABLED)) {
			link_top(graph) = link_top(graph)->next;
			continue;
		}

		/* Get the entity in the other end of the link . */
		next = media_entity_other(entity, link);
		if (WARN_ON(media_entity_id(next) >= MEDIA_ENTITY_ENUM_MAX_ID))
			return NULL;

		/* Has the entity already been visited? */
		if (__test_and_set_bit(media_entity_id(next), graph->entities)) {
			link_top(graph) = link_top(graph)->next;
			continue;
		}

		/* Push the new entity to stack and start over. */
		link_top(graph) = link_top(graph)->next;
		stack_push(graph, next);
	}

	return stack_pop(graph);
}
EXPORT_SYMBOL_GPL(media_entity_graph_walk_next);

/* -----------------------------------------------------------------------------
 * Pipeline management
 */

/**
 * media_entity_pipeline_start - Mark a pipeline as streaming
 * @entity: Starting entity
 * @pipe: Media pipeline to be assigned to all entities in the pipeline.
 *
 * Mark all entities connected to a given entity through enabled links, either
 * directly or indirectly, as streaming. The given pipeline object is assigned to
 * every entity in the pipeline and stored in the media_entity pipe field.
 *
 * Calls to this function can be nested, in which case the same number of
 * media_entity_pipeline_stop() calls will be required to stop streaming. The
 * pipeline pointer must be identical for all nested calls to
 * media_entity_pipeline_start().
 */
__must_check int media_entity_pipeline_start(struct media_entity *entity,
					     struct media_pipeline *pipe)
{
	struct media_device *mdev = entity->graph_obj.mdev;
	struct media_entity_graph graph;
	struct media_entity *entity_err = entity;
	struct media_link *link;
	int ret;

	mutex_lock(&mdev->graph_mutex);

	media_entity_graph_walk_start(&graph, entity);

	while ((entity = media_entity_graph_walk_next(&graph))) {
		DECLARE_BITMAP(active, MEDIA_ENTITY_MAX_PADS);
		DECLARE_BITMAP(has_no_links, MEDIA_ENTITY_MAX_PADS);

		entity->stream_count++;
		WARN_ON(entity->pipe && entity->pipe != pipe);
		entity->pipe = pipe;

		/* Already streaming --- no need to check. */
		if (entity->stream_count > 1)
			continue;

		if (!entity->ops || !entity->ops->link_validate)
			continue;

		bitmap_zero(active, entity->num_pads);
		bitmap_fill(has_no_links, entity->num_pads);

		list_for_each_entry(link, &entity->links, list) {
			struct media_pad *pad = link->sink->entity == entity
						? link->sink : link->source;

			/* Mark that a pad is connected by a link. */
			bitmap_clear(has_no_links, pad->index, 1);

			/*
			 * Pads that either do not need to connect or
			 * are connected through an enabled link are
			 * fine.
			 */
			if (!(pad->flags & MEDIA_PAD_FL_MUST_CONNECT) ||
			    link->flags & MEDIA_LNK_FL_ENABLED)
				bitmap_set(active, pad->index, 1);

			/*
			 * Link validation will only take place for
			 * sink ends of the link that are enabled.
			 */
			if (link->sink != pad ||
			    !(link->flags & MEDIA_LNK_FL_ENABLED))
				continue;

			ret = entity->ops->link_validate(link);
			if (ret < 0 && ret != -ENOIOCTLCMD) {
				dev_dbg(entity->graph_obj.mdev->dev,
					"link validation failed for \"%s\":%u -> \"%s\":%u, error %d\n",
					link->source->entity->name,
					link->source->index,
					entity->name, link->sink->index, ret);
				goto error;
			}
		}

		/* Either no links or validated links are fine. */
		bitmap_or(active, active, has_no_links, entity->num_pads);

		if (!bitmap_full(active, entity->num_pads)) {
			ret = -EPIPE;
			dev_dbg(entity->graph_obj.mdev->dev,
				"\"%s\":%u must be connected by an enabled link\n",
				entity->name,
				(unsigned)find_first_zero_bit(
					active, entity->num_pads));
			goto error;
		}
	}

	mutex_unlock(&mdev->graph_mutex);

	return 0;

error:
	/*
	 * Link validation on graph failed. We revert what we did and
	 * return the error.
	 */
	media_entity_graph_walk_start(&graph, entity_err);

	while ((entity_err = media_entity_graph_walk_next(&graph))) {
		entity_err->stream_count--;
		if (entity_err->stream_count == 0)
			entity_err->pipe = NULL;

		/*
		 * We haven't increased stream_count further than this
		 * so we quit here.
		 */
		if (entity_err == entity)
			break;
	}

	mutex_unlock(&mdev->graph_mutex);

	return ret;
}
EXPORT_SYMBOL_GPL(media_entity_pipeline_start);

/**
 * media_entity_pipeline_stop - Mark a pipeline as not streaming
 * @entity: Starting entity
 *
 * Mark all entities connected to a given entity through enabled links, either
 * directly or indirectly, as not streaming. The media_entity pipe field is
 * reset to NULL.
 *
 * If multiple calls to media_entity_pipeline_start() have been made, the same
 * number of calls to this function are required to mark the pipeline as not
 * streaming.
 */
void media_entity_pipeline_stop(struct media_entity *entity)
{
	struct media_device *mdev = entity->graph_obj.mdev;
	struct media_entity_graph graph;

	mutex_lock(&mdev->graph_mutex);

	media_entity_graph_walk_start(&graph, entity);

	while ((entity = media_entity_graph_walk_next(&graph))) {
		entity->stream_count--;
		if (entity->stream_count == 0)
			entity->pipe = NULL;
	}

	mutex_unlock(&mdev->graph_mutex);
}
EXPORT_SYMBOL_GPL(media_entity_pipeline_stop);

/* -----------------------------------------------------------------------------
 * Module use count
 */

/*
 * media_entity_get - Get a reference to the parent module
 * @entity: The entity
 *
 * Get a reference to the parent media device module.
 *
 * The function will return immediately if @entity is NULL.
 *
 * Return a pointer to the entity on success or NULL on failure.
 */
struct media_entity *media_entity_get(struct media_entity *entity)
{
	if (entity == NULL)
		return NULL;

	if (entity->graph_obj.mdev->dev &&
	    !try_module_get(entity->graph_obj.mdev->dev->driver->owner))
		return NULL;

	return entity;
}
EXPORT_SYMBOL_GPL(media_entity_get);

/*
 * media_entity_put - Release the reference to the parent module
 * @entity: The entity
 *
 * Release the reference count acquired by media_entity_get().
 *
 * The function will return immediately if @entity is NULL.
 */
void media_entity_put(struct media_entity *entity)
{
	if (entity == NULL)
		return;

	if (entity->graph_obj.mdev->dev)
		module_put(entity->graph_obj.mdev->dev->driver->owner);
}
EXPORT_SYMBOL_GPL(media_entity_put);

/* -----------------------------------------------------------------------------
 * Links management
 */

static struct media_link *media_add_link(struct list_head *head)
{
	struct media_link *link;

	link = kzalloc(sizeof(*link), GFP_KERNEL);
	if (link == NULL)
		return NULL;

	list_add_tail(&link->list, head);

	return link;
}

static void __media_entity_remove_link(struct media_entity *entity,
				       struct media_link *link);

int
media_create_pad_link(struct media_entity *source, u16 source_pad,
			 struct media_entity *sink, u16 sink_pad, u32 flags)
{
	struct media_link *link;
	struct media_link *backlink;

	BUG_ON(source == NULL || sink == NULL);
	BUG_ON(source_pad >= source->num_pads);
	BUG_ON(sink_pad >= sink->num_pads);

	link = media_add_link(&source->links);
	if (link == NULL)
		return -ENOMEM;

	link->source = &source->pads[source_pad];
	link->sink = &sink->pads[sink_pad];
	link->flags = flags;

	/* Initialize graph object embedded at the new link */
	media_gobj_init(source->graph_obj.mdev, MEDIA_GRAPH_LINK,
			&link->graph_obj);

	/* Create the backlink. Backlinks are used to help graph traversal and
	 * are not reported to userspace.
	 */
	backlink = media_add_link(&sink->links);
	if (backlink == NULL) {
		__media_entity_remove_link(source, link);
		return -ENOMEM;
	}

	backlink->source = &source->pads[source_pad];
	backlink->sink = &sink->pads[sink_pad];
	backlink->flags = flags;

	/* Initialize graph object embedded at the new link */
	media_gobj_init(sink->graph_obj.mdev, MEDIA_GRAPH_LINK,
			&backlink->graph_obj);

	link->reverse = backlink;
	backlink->reverse = link;

	sink->num_backlinks++;
	sink->num_links++;
	source->num_links++;

	return 0;
}
EXPORT_SYMBOL_GPL(media_create_pad_link);

static void __media_entity_remove_link(struct media_entity *entity,
				       struct media_link *link)
{
	struct media_link *rlink, *tmp;
	struct media_entity *remote;
	unsigned int r = 0;

	if (link->source->entity == entity)
		remote = link->sink->entity;
	else
		remote = link->source->entity;

	list_for_each_entry_safe(rlink, tmp, &remote->links, list) {
		if (rlink != link->reverse) {
			r++;
			continue;
		}

		if (link->source->entity == entity)
			remote->num_backlinks--;

		if (--remote->num_links == 0)
			break;

		/* Remove the remote link */
		list_del(&rlink->list);
		kfree(rlink);
	}
	list_del(&link->list);
	kfree(link);
}

void __media_entity_remove_links(struct media_entity *entity)
{
	struct media_link *link, *tmp;

	list_for_each_entry_safe(link, tmp, &entity->links, list)
		__media_entity_remove_link(entity, link);

	entity->num_links = 0;
	entity->num_backlinks = 0;
}
EXPORT_SYMBOL_GPL(__media_entity_remove_links);

void media_entity_remove_links(struct media_entity *entity)
{
	/* Do nothing if the entity is not registered. */
	if (entity->graph_obj.mdev == NULL)
		return;

	mutex_lock(&entity->graph_obj.mdev->graph_mutex);
	__media_entity_remove_links(entity);
	mutex_unlock(&entity->graph_obj.mdev->graph_mutex);
}
EXPORT_SYMBOL_GPL(media_entity_remove_links);

static int __media_entity_setup_link_notify(struct media_link *link, u32 flags)
{
	int ret;

	/* Notify both entities. */
	ret = media_entity_call(link->source->entity, link_setup,
				link->source, link->sink, flags);
	if (ret < 0 && ret != -ENOIOCTLCMD)
		return ret;

	ret = media_entity_call(link->sink->entity, link_setup,
				link->sink, link->source, flags);
	if (ret < 0 && ret != -ENOIOCTLCMD) {
		media_entity_call(link->source->entity, link_setup,
				  link->source, link->sink, link->flags);
		return ret;
	}

	link->flags = flags;
	link->reverse->flags = link->flags;

	return 0;
}

/**
 * __media_entity_setup_link - Configure a media link
 * @link: The link being configured
 * @flags: Link configuration flags
 *
 * The bulk of link setup is handled by the two entities connected through the
 * link. This function notifies both entities of the link configuration change.
 *
 * If the link is immutable or if the current and new configuration are
 * identical, return immediately.
 *
 * The user is expected to hold link->source->parent->mutex. If not,
 * media_entity_setup_link() should be used instead.
 */
int __media_entity_setup_link(struct media_link *link, u32 flags)
{
	const u32 mask = MEDIA_LNK_FL_ENABLED;
	struct media_device *mdev;
	struct media_entity *source, *sink;
	int ret = -EBUSY;

	if (link == NULL)
		return -EINVAL;

	/* The non-modifiable link flags must not be modified. */
	if ((link->flags & ~mask) != (flags & ~mask))
		return -EINVAL;

	if (link->flags & MEDIA_LNK_FL_IMMUTABLE)
		return link->flags == flags ? 0 : -EINVAL;

	if (link->flags == flags)
		return 0;

	source = link->source->entity;
	sink = link->sink->entity;

	if (!(link->flags & MEDIA_LNK_FL_DYNAMIC) &&
	    (source->stream_count || sink->stream_count))
		return -EBUSY;

	mdev = source->graph_obj.mdev;

	if (mdev->link_notify) {
		ret = mdev->link_notify(link, flags,
					MEDIA_DEV_NOTIFY_PRE_LINK_CH);
		if (ret < 0)
			return ret;
	}

	ret = __media_entity_setup_link_notify(link, flags);

	if (mdev->link_notify)
		mdev->link_notify(link, flags, MEDIA_DEV_NOTIFY_POST_LINK_CH);

	return ret;
}

int media_entity_setup_link(struct media_link *link, u32 flags)
{
	int ret;

	mutex_lock(&link->source->entity->graph_obj.mdev->graph_mutex);
	ret = __media_entity_setup_link(link, flags);
	mutex_unlock(&link->source->entity->graph_obj.mdev->graph_mutex);

	return ret;
}
EXPORT_SYMBOL_GPL(media_entity_setup_link);

/**
 * media_entity_find_link - Find a link between two pads
 * @source: Source pad
 * @sink: Sink pad
 *
 * Return a pointer to the link between the two entities. If no such link
 * exists, return NULL.
 */
struct media_link *
media_entity_find_link(struct media_pad *source, struct media_pad *sink)
{
	struct media_link *link;

	list_for_each_entry(link, &source->entity->links, list) {
		if (link->source->entity == source->entity &&
		    link->source->index == source->index &&
		    link->sink->entity == sink->entity &&
		    link->sink->index == sink->index)
			return link;
	}

	return NULL;
}
EXPORT_SYMBOL_GPL(media_entity_find_link);

/**
 * media_entity_remote_pad - Find the pad at the remote end of a link
 * @pad: Pad at the local end of the link
 *
 * Search for a remote pad connected to the given pad by iterating over all
 * links originating or terminating at that pad until an enabled link is found.
 *
 * Return a pointer to the pad at the remote end of the first found enabled
 * link, or NULL if no enabled link has been found.
 */
struct media_pad *media_entity_remote_pad(struct media_pad *pad)
{
	struct media_link *link;

	list_for_each_entry(link, &pad->entity->links, list) {
		if (!(link->flags & MEDIA_LNK_FL_ENABLED))
			continue;

		if (link->source == pad)
			return link->sink;

		if (link->sink == pad)
			return link->source;
	}

	return NULL;

}
EXPORT_SYMBOL_GPL(media_entity_remote_pad);


static void media_interface_init(struct media_device *mdev,
				 struct media_interface *intf,
				 u32 gobj_type,
				 u32 intf_type, u32 flags)
{
	intf->type = intf_type;
	intf->flags = flags;
	INIT_LIST_HEAD(&intf->links);

	media_gobj_init(mdev, gobj_type, &intf->graph_obj);
}

/* Functions related to the media interface via device nodes */

struct media_intf_devnode *media_devnode_create(struct media_device *mdev,
						u32 type, u32 flags,
						u32 major, u32 minor,
						gfp_t gfp_flags)
{
	struct media_intf_devnode *devnode;

	devnode = kzalloc(sizeof(*devnode), gfp_flags);
	if (!devnode)
		return NULL;

	devnode->major = major;
	devnode->minor = minor;

	media_interface_init(mdev, &devnode->intf, MEDIA_GRAPH_INTF_DEVNODE,
			     type, flags);

	return devnode;
}
EXPORT_SYMBOL_GPL(media_devnode_create);

void media_devnode_remove(struct media_intf_devnode *devnode)
{
	media_gobj_remove(&devnode->intf.graph_obj);
	kfree(devnode);
}
EXPORT_SYMBOL_GPL(media_devnode_remove);

struct media_link *media_create_intf_link(struct media_entity *entity,
					    struct media_interface *intf,
					    u32 flags)
{
	struct media_link *link;

	link = media_add_link(&intf->links);
	if (link == NULL)
		return NULL;

	link->intf = intf;
	link->entity = entity;
	link->flags = flags;

	/* Initialize graph object embedded at the new link */
	media_gobj_init(intf->graph_obj.mdev, MEDIA_GRAPH_LINK,
			&link->graph_obj);

	return link;
}
EXPORT_SYMBOL_GPL(media_create_intf_link);


static void __media_remove_intf_link(struct media_link *link)
{
	media_gobj_remove(&link->graph_obj);
	kfree(link);
}

void media_remove_intf_link(struct media_link *link)
{
	mutex_lock(&link->graph_obj.mdev->graph_mutex);
	__media_remove_intf_link(link);
	mutex_unlock(&link->graph_obj.mdev->graph_mutex);
}
EXPORT_SYMBOL_GPL(media_remove_intf_link);