[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>

Documentation/DocBook/media/v4l/vidioc-enum-fmt.xml

@@ -58,6 +58,9 @@ structure. Drivers fill the rest of the structure or return an
 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">

Documentation/DocBook/media/v4l/vidioc-g-fmt.xml

@@ -81,7 +81,7 @@ the application calls the <constant>VIDIOC_S_FMT</constant> ioctl
 with a pointer to a <structname>v4l2_format</structname> structure
 the driver checks
 and adjusts the parameters against hardware abilities. Drivers
-should not return an error code unless the input is ambiguous, this is
+should not return an error code unless the <structfield>type</structfield> field is invalid, this is
 a mechanism to fathom device capabilities and to approach parameters
 acceptable for both the application and driver. On success the driver
 may program the hardware, allocate resources and generally prepare for
@@ -107,6 +107,10 @@ disabling I/O or possibly time consuming hardware preparations.
 Although strongly recommended drivers are not required to implement
 this ioctl.</para>
 
+    <para>The format as returned by <constant>VIDIOC_TRY_FMT</constant>
+must be identical to what <constant>VIDIOC_S_FMT</constant> returns for
+the same input or output.</para>
+
     <table pgwide="1" frame="none" id="v4l2-format">
       <title>struct <structname>v4l2_format</structname></title>
       <tgroup cols="4">
@@ -187,8 +191,7 @@ capture and output devices.</entry>
 	<term><errorcode>EINVAL</errorcode></term>
 	<listitem>
 	  <para>The &v4l2-format; <structfield>type</structfield>
-field is invalid, the requested buffer type not supported, or the
-format is not supported with this buffer type.</para>
+field is invalid or the requested buffer type not supported.</para>
 	</listitem>
       </varlistentry>
     </variablelist>