3 files changed, 77 insertions, 4 deletions

diff --git a/Documentation/media-framework.txt b/Documentation/media-framework.txt
index 3a0f879533ce..802875413873 100644
--- a/Documentation/media-framework.txt
+++ b/Documentation/media-framework.txt
@@ -335,6 +335,9 @@ the media_entity pipe field.
 Calls to media_entity_pipeline_start() can be nested. The pipeline pointer must
 be identical for all nested calls to the function.
 
+media_entity_pipeline_start() may return an error. In that case, it will
+clean up any the changes it did by itself.
+
 When stopping the stream, drivers must notify the entities with
 
         media_entity_pipeline_stop(struct media_entity *entity);
@@ -351,3 +354,19 @@ If other operations need to be disallowed on streaming entities (such as
 changing entities configuration parameters) drivers can explicitly check the
 media_entity stream_count field to find out if an entity is streaming. This
 operation must be done with the media_device graph_mutex held.
+
+
+Link validation
+---------------
+
+Link validation is performed by media_entity_pipeline_start() for any
+entity which has sink pads in the pipeline. The
+media_entity::link_validate() callback is used for that purpose. In
+link_validate() callback, entity driver should check that the properties of
+the source pad of the connected entity and its own sink pad match. It is up
+to the type of the entity (and in the end, the properties of the hardware)
+what matching actually means.
+
+Subsystems should facilitate link validation by providing subsystem specific
+helper functions to provide easy access for commonly needed information, and
+in the end provide a way to use driver-specific callbacks.
diff --git a/drivers/media/media-entity.c b/drivers/media/media-entity.c
index 056138f63c7d..e1cd13283407 100644
--- a/drivers/media/media-entity.c
+++ b/drivers/media/media-entity.c
@@ -214,23 +214,76 @@ EXPORT_SYMBOL_GPL(media_entity_graph_walk_next);
  * pipeline pointer must be identical for all nested calls to
  * media_entity_pipeline_start().
  */
-void media_entity_pipeline_start(struct media_entity *entity,
-                                 struct media_pipeline *pipe)
+__must_check int media_entity_pipeline_start(struct media_entity *entity,
+                                             struct media_pipeline *pipe)
 {
         struct media_device *mdev = entity->parent;
         struct media_entity_graph graph;
+        struct media_entity *entity_err = entity;
+        int ret;
 
         mutex_lock(&mdev->graph_mutex);
 
         media_entity_graph_walk_start(&graph, entity);
 
         while ((entity = media_entity_graph_walk_next(&graph))) {
+                unsigned int i;
+
                 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;
+
+                for (i = 0; i < entity->num_links; i++) {
+                        struct media_link *link = &entity->links[i];
+
+                        /* Is this pad part of an enabled link? */
+                        if (!(link->flags & MEDIA_LNK_FL_ENABLED))
+                                continue;
+
+                        /* Are we the sink or not? */
+                        if (link->sink->entity != entity)
+                                continue;
+
+                        ret = entity->ops->link_validate(link);
+                        if (ret < 0 && ret != -ENOIOCTLCMD)
+                                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);
 
diff --git a/include/media/media-entity.h b/include/media/media-entity.h
index 29e7bba78ffe..0c16f518ee09 100644
--- a/include/media/media-entity.h
+++ b/include/media/media-entity.h
@@ -46,6 +46,7 @@ struct media_entity_operations {
         int (*link_setup)(struct media_entity *entity,
                           const struct media_pad *local,
                           const struct media_pad *remote, u32 flags);
+        int (*link_validate)(struct media_link *link);
 };
 
 struct media_entity {
@@ -140,8 +141,8 @@ void media_entity_graph_walk_start(struct media_entity_graph *graph,
                 struct media_entity *entity);
 struct media_entity *
 media_entity_graph_walk_next(struct media_entity_graph *graph);
-void media_entity_pipeline_start(struct media_entity *entity,
-                struct media_pipeline *pipe);
+__must_check int media_entity_pipeline_start(struct media_entity *entity,
+                                             struct media_pipeline *pipe);
 void media_entity_pipeline_stop(struct media_entity *entity);
 
 #define media_entity_call(entity, operation, args...)                   \