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Diffstat (limited to 'Documentation/media-framework.txt')
| -rw-r--r-- | Documentation/media-framework.txt | 42 |
1 files changed, 42 insertions, 0 deletions
diff --git a/Documentation/media-framework.txt b/Documentation/media-framework.txt index 0257bad2a10..ab17f33dded 100644 --- a/Documentation/media-framework.txt +++ b/Documentation/media-framework.txt @@ -216,3 +216,45 @@ Links have flags that describe the link capabilities and state. modified at runtime. If MEDIA_LNK_FL_IMMUTABLE is set, then MEDIA_LNK_FL_ENABLED must also be set since an immutable link is always enabled. + + +Graph traversal +--------------- + +The media framework provides APIs to iterate over entities in a graph. + +To iterate over all entities belonging to a media device, drivers can use the +media_device_for_each_entity macro, defined in include/media/media-device.h. + + struct media_entity *entity; + + media_device_for_each_entity(entity, mdev) { + /* entity will point to each entity in turn */ + ... + } + +Drivers might also need to iterate over all entities in a graph that can be +reached only through enabled links starting at a given entity. The media +framework provides a depth-first graph traversal API for that purpose. + +Note that graphs with cycles (whether directed or undirected) are *NOT* +supported by the graph traversal API. To prevent infinite loops, the graph +traversal code limits the maximum depth to MEDIA_ENTITY_ENUM_MAX_DEPTH, +currently defined as 16. + +Drivers initiate a graph traversal by calling + + media_entity_graph_walk_start(struct media_entity_graph *graph, + struct media_entity *entity); + +The graph structure, provided by the caller, is initialized to start graph +traversal at the given entity. + +Drivers can then retrieve the next entity by calling + + media_entity_graph_walk_next(struct media_entity_graph *graph); + +When the graph traversal is complete the function will return NULL. + +Graph traversal can be interrupted at any moment. No cleanup function call is +required and the graph structure can be freed normally. |