[PATCH v5 1/9] media: Add support for circular graph traversal

[Laurent Pinchart]

The graph traversal API (media_entity_graph_walk_*) doesn't support
cyclic graphs and will fail to correctly walk a graph when circular
links exist. Support circular graph traversal by checking whether an
entity has already been visited before pushing it to the stack.

Signed-off-by: Laurent Pinchart <laurent.pinchart+rene...@ideasonboard.com>
Acked-by: Sakari Ailus <sakari.ai...@iki.fi>
---
 drivers/media/media-entity.c | 14 +++++++++++---
 include/media/media-entity.h |  4 ++++
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/media/media-entity.c b/drivers/media/media-entity.c
index cb30ffb..2c286c3 100644
--- a/drivers/media/media-entity.c
+++ b/drivers/media/media-entity.c
@@ -20,6 +20,7 @@
  * 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>
@@ -121,7 +122,6 @@ static struct media_entity *stack_pop(struct 
media_entity_graph *graph)
        return entity;
 }
 
-#define stack_peek(en) ((en)->stack[(en)->top - 1].entity)
 #define link_top(en)   ((en)->stack[(en)->top].link)
 #define stack_top(en)  ((en)->stack[(en)->top].entity)
 
@@ -140,6 +140,12 @@ void media_entity_graph_walk_start(struct 
media_entity_graph *graph,
 {
        graph->top = 0;
        graph->stack[graph->top].entity = NULL;
+       bitmap_zero(graph->entities, MEDIA_ENTITY_ENUM_MAX_ID);
+
+       if (WARN_ON(entity->id >= MEDIA_ENTITY_ENUM_MAX_ID))
+               return;
+
+       __set_bit(entity->id, graph->entities);
        stack_push(graph, entity);
 }
 EXPORT_SYMBOL_GPL(media_entity_graph_walk_start);
@@ -180,9 +186,11 @@ media_entity_graph_walk_next(struct media_entity_graph 
*graph)
 
                /* Get the entity in the other end of the link . */
                next = media_entity_other(entity, link);
+               if (WARN_ON(next->id >= MEDIA_ENTITY_ENUM_MAX_ID))
+                       return NULL;
 
-               /* Was it the entity we came here from? */
-               if (next == stack_peek(graph)) {
+               /* Has the entity already been visited? */
+               if (__test_and_set_bit(next->id, graph->entities)) {
                        link_top(graph)++;
                        continue;
                }
diff --git a/include/media/media-entity.h b/include/media/media-entity.h
index 06bacf9..10df551 100644
--- a/include/media/media-entity.h
+++ b/include/media/media-entity.h
@@ -23,6 +23,7 @@
 #ifndef _MEDIA_ENTITY_H
 #define _MEDIA_ENTITY_H
 
+#include <linux/bitops.h>
 #include <linux/list.h>
 #include <linux/media.h>
 
@@ -113,12 +114,15 @@ static inline u32 media_entity_subtype(struct 
media_entity *entity)
 }
 
 #define MEDIA_ENTITY_ENUM_MAX_DEPTH    16
+#define MEDIA_ENTITY_ENUM_MAX_ID       64
 
 struct media_entity_graph {
        struct {
                struct media_entity *entity;
                int link;
        } stack[MEDIA_ENTITY_ENUM_MAX_DEPTH];
+
+       DECLARE_BITMAP(entities, MEDIA_ENTITY_ENUM_MAX_ID);
        int top;
 };
 
-- 
1.8.1.5

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