V4L/DVB: Add documentation for the new error flag

Add documentation for V4L2_BUF_FLAG_ERROR.

Signed-off-by: Pawel Osciak <p.osciak@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

2 files changed, 22 insertions, 2 deletions

diff --git a/Documentation/DocBook/v4l/io.xml b/Documentation/DocBook/v4l/io.xml
index bb685ed6fe7b..d424886beda0 100644
--- a/Documentation/DocBook/v4l/io.xml
+++ b/Documentation/DocBook/v4l/io.xml
@@ -702,6 +702,16 @@ They can be both cleared however, then the buffer is in "dequeued"
 state, in the application domain to say so.</entry>
           </row>
           <row>
+            <entry><constant>V4L2_BUF_FLAG_ERROR</constant></entry>
+            <entry>0x0040</entry>
+            <entry>When this flag is set, the buffer has been dequeued
+            successfully, although the data might have been corrupted.
+            This is recoverable, streaming may continue as normal and
+            the buffer may be reused normally.
+            Drivers set this flag when the <constant>VIDIOC_DQBUF</constant>
+            ioctl is called.</entry>
+          </row>
+          <row>
             <entry><constant>V4L2_BUF_FLAG_KEYFRAME</constant></entry>
             <entry>0x0008</entry>
           <entry>Drivers set or clear this flag when calling the
diff --git a/Documentation/DocBook/v4l/vidioc-qbuf.xml b/Documentation/DocBook/v4l/vidioc-qbuf.xml
index b843bd7b3897..ab691ebf3b93 100644
--- a/Documentation/DocBook/v4l/vidioc-qbuf.xml
+++ b/Documentation/DocBook/v4l/vidioc-qbuf.xml
@@ -111,7 +111,11 @@ from the driver's outgoing queue. They just set the
 and <structfield>reserved</structfield>
 fields of a &v4l2-buffer; as above, when <constant>VIDIOC_DQBUF</constant>
 is called with a pointer to this structure the driver fills the
-remaining fields or returns an error code.</para>
+remaining fields or returns an error code. The driver may also set
+<constant>V4L2_BUF_FLAG_ERROR</constant> in the <structfield>flags</structfield>
+field. It indicates a non-critical (recoverable) streaming error. In such case
+the application may continue as normal, but should be aware that data in the
+dequeued buffer might be corrupted.</para>
 
     <para>By default <constant>VIDIOC_DQBUF</constant> blocks when no
 buffer is in the outgoing queue. When the
@@ -158,7 +162,13 @@ enqueue a user pointer buffer.</para>
           <para><constant>VIDIOC_DQBUF</constant> failed due to an
 internal error. Can also indicate temporary problems like signal
 loss. Note the driver might dequeue an (empty) buffer despite
-returning an error, or even stop capturing.</para>
+returning an error, or even stop capturing. Reusing such buffer may be unsafe
+though and its details (e.g. <structfield>index</structfield>) may not be
+returned either. It is recommended that drivers indicate recoverable errors
+by setting the <constant>V4L2_BUF_FLAG_ERROR</constant> and returning 0 instead.
+In that case the application should be able to safely reuse the buffer and
+continue streaming.
+        </para>
         </listitem>
       </varlistentry>
     </variablelist>