media: vidioc-dqevent.rst: clarify V4L2_EVENT_SRC_CH_RESOLUTION

Clarify that when you receive V4L2_EVENT_SOURCE_CHANGE with flag
V4L2_EVENT_SRC_CH_RESOLUTION set, and the new resolution appears
identical to the old resolution, then you still must restart the
streaming I/O.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

diff --git a/Documentation/media/uapi/v4l/vidioc-dqevent.rst b/Documentation/media/uapi/v4l/vidioc-dqevent.rst
index cb3565f367933f0b983f2d292400856ac6f50fd2..04416b6943c0bd53ab9f4d72b65e9f4c751032bc 100644 (file)
--- a/Documentation/media/uapi/v4l/vidioc-dqevent.rst
+++ b/Documentation/media/uapi/v4l/vidioc-dqevent.rst
@@ -379,7 +379,17 @@ call.
       - 0x0001
       - This event gets triggered when a resolution change is detected at
        an input. This can come from an input connector or from a video
-       decoder.
+       decoder. Applications will have to query the new resolution (if
+       any, the signal may also have been lost).
+
+       *Important*: even if the new video timings appear identical to the old
+       ones, receiving this event indicates that there was an issue with the
+       video signal and you must stop and restart streaming
+       (:ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>`
+       followed by :ref:`VIDIOC_STREAMON <VIDIOC_STREAMON>`). The reason is
+       that many devices are not able to recover from a temporary loss of
+       signal and so restarting streaming I/O is required in order for the
+       hardware to synchronize to the video signal.
 
 
 Return Value