1 files changed, 22 insertions, 0 deletions
diff --git a/Documentation/userspace-api/media/v4l/dv-timings.rst b/Documentation/userspace-api/media/v4l/dv-timings.rst
index e17f056b129f..9f117c82df1b 100644
--- a/Documentation/userspace-api/media/v4l/dv-timings.rst
+++ b/Documentation/userspace-api/media/v4l/dv-timings.rst
@@ -1,4 +1,5 @@
 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
+.. c:namespace:: V4L
 
 .. _dv-timings:
 
@@ -33,6 +34,27 @@ current DV timings they use the
 the DV timings as seen by the video receiver applications use the
 :ref:`VIDIOC_QUERY_DV_TIMINGS` ioctl.
 
+When the hardware detects a video source change (e.g. the video
+signal appears or disappears, or the video resolution changes), then
+it will issue a `V4L2_EVENT_SOURCE_CHANGE` event. Use the
+:ref:`ioctl VIDIOC_SUBSCRIBE_EVENT <VIDIOC_SUBSCRIBE_EVENT>` and the
+:ref:`VIDIOC_DQEVENT` to check if this event was reported.
+
+If the video signal changed, then the application has to stop
+streaming, free all buffers, and call the :ref:`VIDIOC_QUERY_DV_TIMINGS`
+to obtain the new video timings, and if they are valid, it can set
+those by calling the :ref:`ioctl VIDIOC_S_DV_TIMINGS <VIDIOC_G_DV_TIMINGS>`.
+This will also update the format, so use the :ref:`ioctl VIDIOC_G_FMT <VIDIOC_G_FMT>`
+to obtain the new format. Now the application can allocate new buffers
+and start streaming again.
+
+The :ref:`VIDIOC_QUERY_DV_TIMINGS` will just report what the
+hardware detects, it will never change the configuration. If the
+currently set timings and the actually detected timings differ, then
+typically this will mean that you will not be able to capture any
+video. The correct approach is to rely on the `V4L2_EVENT_SOURCE_CHANGE`
+event so you know when something changed.
+
 Applications can make use of the :ref:`input-capabilities` and
 :ref:`output-capabilities` flags to determine whether the digital
 video ioctls can be used with the given input or output.