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authorSakari Ailus <sakari.ailus@iki.fi>2012-01-11 06:25:15 -0300
committerMauro Carvalho Chehab <mchehab@redhat.com>2012-05-14 08:44:11 -0300
commitaf88be3887c1a0b20d0792c3c237a67c73ef3286 (patch)
tree79047160436c63bab20241807a61d8030b6a0527 /Documentation/media-framework.txt
parent440f0fadd407c66abe285ce26ed8c31fb2403f0d (diff)
[media] media: Add link_validate() op to check links to the sink pad
The purpose of the link_validate() op is to allow an entity driver to ensure that the properties of the pads at the both ends of the link are suitable for starting the pipeline. link_validate is called on sink pads on active links which belong to the active part of the graph. Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi> Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Diffstat (limited to 'Documentation/media-framework.txt')
-rw-r--r--Documentation/media-framework.txt19
1 files changed, 19 insertions, 0 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.