[media] DocBook: make the G/S/TRY_FMT specification more strict

- S/TRY_FMT should always succeed, unless an invalid type field is passed in.
- TRY_FMT should give the same result as S_FMT, all other things being equal.
- ENUMFMT may return different formats for different inputs or outputs.
This was decided during the 2012 Media Workshop.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Sakari Ailus <sakari.ailus@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
diff --git a/Documentation/DocBook/media/v4l/vidioc-enum-fmt.xml b/Documentation/DocBook/media/v4l/vidioc-enum-fmt.xml
index 81ebe48..0bd3324 100644
--- a/Documentation/DocBook/media/v4l/vidioc-enum-fmt.xml
+++ b/Documentation/DocBook/media/v4l/vidioc-enum-fmt.xml
@@ -58,6 +58,9 @@
 incrementing by one until <errorcode>EINVAL</errorcode> is
 returned.</para>
 
+    <para>Note that after switching input or output the list of enumerated image
+formats may be different.</para>
+
     <table pgwide="1" frame="none" id="v4l2-fmtdesc">
       <title>struct <structname>v4l2_fmtdesc</structname></title>
       <tgroup cols="3">