[media] media: convert links from array to list

The entire logic that represent graph links were developed on a
time where there were no needs to dynamic remove links. So,
although links are created/removed one by one via some
functions, they're stored as an array inside the entity struct.

As the array may grow, there's a logic inside the code that
checks if the amount of space is not enough to store
the needed links. If it isn't the core uses krealloc()
to change the size of the link, with is bad, as it
leaves the memory fragmented.

So, convert links into a list.

Also, currently,  both source and sink entities need the link
at the graph traversal logic inside media_entity. So there's
a logic duplicating all links. That makes it to spend
twice the memory needed. This is not a big deal for today's
usage, where the number of links are not big.

Yet, if during the MC workshop discussions, it was said that
IIO graphs could have up to 4,000 entities. So, we may
want to remove the duplication on some future. The problem
is that it would require a separate linked list to store
the backlinks inside the entity, or to use a more complex
algorithm to do graph backlink traversal, with is something
that the current graph traversal inside the core can't cope
with. So, let's postpone a such change if/when it is actually
needed.

It should also be noticed that the media_link structure uses
44 bytes on 32-bit architectures and 84 bytes on 64-bit
architecture. It will thus be allocated out of the 64-bytes and
96-bytes pools respectively. That's a 12.5% memory waste on
64-bit architectures and 31.25% on 32-bit architecture.
A linked list is less efficient than an array in this case, but
this could later be optimized if we can get rid of the reverse
links (with would reduce memory allocation by 50%).

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

1 files changed, 63 insertions, 65 deletions

diff --git a/drivers/media/media-entity.c b/drivers/media/media-entity.c
index f85a711..df110ac 100644
--- a/drivers/media/media-entity.c
+++ b/drivers/media/media-entity.c
@@ -209,21 +209,13 @@ int
 media_entity_init(struct media_entity *entity, u16 num_pads,
 		  struct media_pad *pads)
 {
-	struct media_link *links;
-	unsigned int max_links = num_pads;
 	unsigned int i;
 
-	links = kzalloc(max_links * sizeof(links[0]), GFP_KERNEL);
-	if (links == NULL)
-		return -ENOMEM;
-
 	entity->group_id = 0;
-	entity->max_links = max_links;
 	entity->num_links = 0;
 	entity->num_backlinks = 0;
 	entity->num_pads = num_pads;
 	entity->pads = pads;
-	entity->links = links;
 
 	for (i = 0; i < num_pads; i++) {
 		pads[i].entity = entity;
@@ -237,7 +229,13 @@ EXPORT_SYMBOL_GPL(media_entity_init);
 void
 media_entity_cleanup(struct media_entity *entity)
 {
-	kfree(entity->links);
+	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);
 
@@ -263,7 +261,7 @@ static void stack_push(struct media_entity_graph *graph,
 		return;
 	}
 	graph->top++;
-	graph->stack[graph->top].link = 0;
+	graph->stack[graph->top].link = (&entity->links)->next;
 	graph->stack[graph->top].entity = entity;
 }
 
@@ -305,6 +303,7 @@ void media_entity_graph_walk_start(struct media_entity_graph *graph,
 }
 EXPORT_SYMBOL_GPL(media_entity_graph_walk_start);
 
+
 /**
  * media_entity_graph_walk_next - Get the next entity in the graph
  * @graph: Media graph structure
@@ -328,14 +327,16 @@ media_entity_graph_walk_next(struct media_entity_graph *graph)
 	 * top of the stack until no more entities on the level can be
 	 * found.
 	 */
-	while (link_top(graph) < stack_top(graph)->num_links) {
+	while (link_top(graph) != &(stack_top(graph)->links)) {
 		struct media_entity *entity = stack_top(graph);
-		struct media_link *link = &entity->links[link_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) = link_top(graph)->next;
 			continue;
 		}
 
@@ -346,12 +347,12 @@ media_entity_graph_walk_next(struct media_entity_graph *graph)
 
 		/* Has the entity already been visited? */
 		if (__test_and_set_bit(media_entity_id(next), graph->entities)) {
-			link_top(graph)++;
+			link_top(graph) = link_top(graph)->next;
 			continue;
 		}
 
 		/* Push the new entity to stack and start over. */
-		link_top(graph)++;
+		link_top(graph) = link_top(graph)->next;
 		stack_push(graph, next);
 	}
 
@@ -383,6 +384,7 @@ __must_check int media_entity_pipeline_start(struct media_entity *entity,
 	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);
@@ -392,7 +394,6 @@ __must_check int media_entity_pipeline_start(struct media_entity *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);
-		unsigned int i;
 
 		entity->stream_count++;
 		WARN_ON(entity->pipe && entity->pipe != pipe);
@@ -408,8 +409,7 @@ __must_check int media_entity_pipeline_start(struct media_entity *entity,
 		bitmap_zero(active, entity->num_pads);
 		bitmap_fill(has_no_links, entity->num_pads);
 
-		for (i = 0; i < entity->num_links; i++) {
-			struct media_link *link = &entity->links[i];
+		list_for_each_entry(link, &entity->links, list) {
 			struct media_pad *pad = link->sink->entity == entity
 						? link->sink : link->source;
 
@@ -570,25 +570,20 @@ EXPORT_SYMBOL_GPL(media_entity_put);
 
 static struct media_link *media_entity_add_link(struct media_entity *entity)
 {
-	if (entity->num_links >= entity->max_links) {
-		struct media_link *links = entity->links;
-		unsigned int max_links = entity->max_links + 2;
-		unsigned int i;
-
-		links = krealloc(links, max_links * sizeof(*links), GFP_KERNEL);
-		if (links == NULL)
-			return NULL;
+	struct media_link *link;
 
-		for (i = 0; i < entity->num_links; i++)
-			links[i].reverse->reverse = &links[i];
+	link = kzalloc(sizeof(*link), GFP_KERNEL);
+	if (link == NULL)
+		return NULL;
 
-		entity->max_links = max_links;
-		entity->links = links;
-	}
+	list_add_tail(&link->list, &entity->links);
 
-	return &entity->links[entity->num_links++];
+	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)
@@ -617,7 +612,7 @@ media_create_pad_link(struct media_entity *source, u16 source_pad,
 	 */
 	backlink = media_entity_add_link(sink);
 	if (backlink == NULL) {
-		source->num_links--;
+		__media_entity_remove_link(source, link);
 		return -ENOMEM;
 	}
 
@@ -633,43 +628,51 @@ media_create_pad_link(struct media_entity *source, u16 source_pad,
 	backlink->reverse = link;
 
 	sink->num_backlinks++;
+	sink->num_links++;
+	source->num_links++;
 
 	return 0;
 }
 EXPORT_SYMBOL_GPL(media_create_pad_link);
 
-void __media_entity_remove_links(struct media_entity *entity)
+static void __media_entity_remove_link(struct media_entity *entity,
+				       struct media_link *link)
 {
-	unsigned int i;
+	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;
 
-	for (i = 0; i < entity->num_links; i++) {
-		struct media_link *link = &entity->links[i];
-		struct media_entity *remote;
-		unsigned int r = 0;
+	list_for_each_entry_safe(rlink, tmp, &remote->links, list) {
+		if (rlink != link->reverse) {
+			r++;
+			continue;
+		}
 
 		if (link->source->entity == entity)
-			remote = link->sink->entity;
-		else
-			remote = link->source->entity;
+			remote->num_backlinks--;
 
-		while (r < remote->num_links) {
-			struct media_link *rlink = &remote->links[r];
-
-			if (rlink != link->reverse) {
-				r++;
-				continue;
-			}
+		if (--remote->num_links == 0)
+			break;
 
-			if (link->source->entity == entity)
-				remote->num_backlinks--;
+		/* Remove the remote link */
+		list_del(&rlink->list);
+		kfree(rlink);
+	}
+	list_del(&link->list);
+	kfree(link);
+}
 
-			if (--remote->num_links == 0)
-				break;
+void __media_entity_remove_links(struct media_entity *entity)
+{
+	struct media_link *link, *tmp;
 
-			/* Insert last entry in place of the dropped link. */
-			*rlink = remote->links[remote->num_links];
-		}
-	}
+	list_for_each_entry_safe(link, tmp, &entity->links, list)
+		__media_entity_remove_link(entity, link);
 
 	entity->num_links = 0;
 	entity->num_backlinks = 0;
@@ -794,11 +797,8 @@ struct media_link *
 media_entity_find_link(struct media_pad *source, struct media_pad *sink)
 {
 	struct media_link *link;
-	unsigned int i;
-
-	for (i = 0; i < source->entity->num_links; ++i) {
-		link = &source->entity->links[i];
 
+	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 &&
@@ -822,11 +822,9 @@ EXPORT_SYMBOL_GPL(media_entity_find_link);
  */
 struct media_pad *media_entity_remote_pad(struct media_pad *pad)
 {
-	unsigned int i;
-
-	for (i = 0; i < pad->entity->num_links; i++) {
-		struct media_link *link = &pad->entity->links[i];
+	struct media_link *link;
 
+	list_for_each_entry(link, &pad->entity->links, list) {
 		if (!(link->flags & MEDIA_LNK_FL_ENABLED))
 			continue;