media: videodev2.h: add V4L2_DEC_CMD_FLUSH

Add this new V4L2_DEC_CMD_FLUSH decoder command and document it.
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Alexandre Courbot <acourbot@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

Documentation/media/uapi/v4l/vidioc-decoder-cmd.rst

@@ -208,7 +208,15 @@ introduced in Linux 3.3. They are, however, mandatory for stateful mem2mem decod
 	been started yet, the driver will return an ``EPERM`` error code. When
 	the decoder is already running, this command does nothing. No
 	flags are defined for this command.
-
+    * - ``V4L2_DEC_CMD_FLUSH``
+      - 4
+      - Flush any held capture buffers. Only valid for stateless decoders.
+	This command is typically used when the application reached the
+	end of the stream and the last output buffer had the
+	``V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF`` flag set. This would prevent
+	dequeueing the capture buffer containing the last decoded frame.
+	So this command can be used to explicitly flush that final decoded
+	frame. This command does nothing if there are no held capture buffers.
 
 Return Value
 ============

Documentation/media/videodev2.h.rst.exceptions

@@ -435,6 +435,7 @@ replace define V4L2_DEC_CMD_START decoder-cmds
 replace define V4L2_DEC_CMD_STOP decoder-cmds
 replace define V4L2_DEC_CMD_PAUSE decoder-cmds
 replace define V4L2_DEC_CMD_RESUME decoder-cmds
+replace define V4L2_DEC_CMD_FLUSH decoder-cmds
 
 replace define V4L2_DEC_CMD_START_MUTE_AUDIO decoder-cmds
 replace define V4L2_DEC_CMD_PAUSE_TO_BLACK decoder-cmds

include/uapi/linux/videodev2.h

@@ -1984,6 +1984,7 @@ struct v4l2_encoder_cmd {
 #define V4L2_DEC_CMD_STOP        (1)
 #define V4L2_DEC_CMD_PAUSE       (2)
 #define V4L2_DEC_CMD_RESUME      (3)
+#define V4L2_DEC_CMD_FLUSH       (4)
 
 /* Flags for V4L2_DEC_CMD_START */
 #define V4L2_DEC_CMD_START_MUTE_AUDIO	(1 << 0)