[media] media: Pipelines and media streams

Drivers often need to associate pipeline objects to entities, and to
take stream state into account when configuring entities and links. The
pipeline API helps drivers manage that information.

When starting streaming, drivers call media_entity_pipeline_start(). The
function marks all entities connected to the given entity through
enabled links, either directly or indirectly, as streaming. Similarly,
when stopping the stream, drivers call media_entity_pipeline_stop().

The media_entity_pipeline_start() function takes a pointer to a media
pipeline and stores it in every entity in the graph. Drivers should
embed the media_pipeline structure in higher-level pipeline structures
and can then access the pipeline through the media_entity structure.

Link configuration will fail with -EBUSY by default if either end of the
link is a streaming entity, unless the link is marked with the
MEDIA_LNK_FL_DYNAMIC flag.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

2 files changed, 8 insertions, 0 deletions

diff --git a/Documentation/DocBook/v4l/media-ioc-enum-links.xml b/Documentation/DocBook/v4l/media-ioc-enum-links.xml
index 6da884159cab..d2fc73ef8d56 100644
--- a/Documentation/DocBook/v4l/media-ioc-enum-links.xml
+++ b/Documentation/DocBook/v4l/media-ioc-enum-links.xml
@@ -179,6 +179,11 @@
             <entry>The link enabled state can't be modified at runtime. An
             immutable link is always enabled.</entry>
           </row>
+          <row>
+            <entry><constant>MEDIA_LNK_FL_DYNAMIC</constant></entry>
+            <entry>The link enabled state can be modified during streaming. This
+            flag is set by drivers and is read-only for applications.</entry>
+          </row>
         </tbody>
       </tgroup>
     </table>
diff --git a/Documentation/DocBook/v4l/media-ioc-setup-link.xml b/Documentation/DocBook/v4l/media-ioc-setup-link.xml
index 09ab3d2b3a52..2331e76ded17 100644
--- a/Documentation/DocBook/v4l/media-ioc-setup-link.xml
+++ b/Documentation/DocBook/v4l/media-ioc-setup-link.xml
@@ -60,6 +60,9 @@
     <para>Link configuration has no side effect on other links. If an enabled
     link at the sink pad prevents the link from being enabled, the driver
     returns with an &EBUSY;.</para>
+    <para>Only links marked with the <constant>DYNAMIC</constant> link flag can
+    be enabled/disabled while streaming media data. Attempting to enable or
+    disable a streaming non-dynamic link will return an &EBUSY;.</para>
     <para>If the specified link can't be found the driver returns with an
     &EINVAL;.</para>
   </refsect1>