media: v4l: uAPI doc: Changing frame interval won't change format

Document that changing the frame interval has no effect on frame size.
While this was the assumption in the API, it was not documented as such.
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

Documentation/media/uapi/v4l/vidioc-g-parm.rst

@@ -42,6 +42,9 @@ side. This is especially useful when using the :ref:`read() <func-read>` or
 :ref:`write() <func-write>`, which are not augmented by timestamps or sequence
 counters, and to avoid unnecessary data copying.
 
+Changing the frame interval shall never change the format. Changing the
+format, on the other hand, may change the frame interval.
+
 Further these ioctls can be used to determine the number of buffers used
 internally by a driver in read/write mode. For implications see the
 section discussing the :ref:`read() <func-read>` function.

Documentation/media/uapi/v4l/vidioc-subdev-g-frame-interval.rst

@@ -63,6 +63,9 @@ doesn't match the device capabilities. They must instead modify the
 interval to match what the hardware can provide. The modified interval
 should be as close as possible to the original request.
 
+Changing the frame interval shall never change the format. Changing the
+format, on the other hand, may change the frame interval.
+
 Sub-devices that support the frame interval ioctls should implement them
 on a single pad only. Their behaviour when supported on multiple pads of
 the same sub-device is not defined.