[media] Spec: document CREATE_BUFS behavior if count == 0

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/Documentation/DocBook/media/v4l/vidioc-create-bufs.xml b/Documentation/DocBook/media/v4l/vidioc-create-bufs.xml
index a2474ecb574a..5e73b1c8d095 100644
--- a/Documentation/DocBook/media/v4l/vidioc-create-bufs.xml
+++ b/Documentation/DocBook/media/v4l/vidioc-create-bufs.xml
@@ -97,7 +97,13 @@ information.</para>
           <row>
             <entry>__u32</entry>
             <entry><structfield>count</structfield></entry>
-            <entry>The number of buffers requested or granted.</entry>
+            <entry>The number of buffers requested or granted. If count == 0, then
+            <constant>VIDIOC_CREATE_BUFS</constant> will set <structfield>index</structfield>
+            to the current number of created buffers, and it will check the validity of
+            <structfield>memory</structfield> and <structfield>format.type</structfield>.
+            If those are invalid -1 is returned and errno is set to &EINVAL;,
+            otherwise <constant>VIDIOC_CREATE_BUFS</constant> returns 0. It will
+            never set errno to &EBUSY; in this particular case.</entry>
           </row>
           <row>
             <entry>__u32</entry>