1 files changed, 119 insertions, 0 deletions
diff --git a/Documentation/userspace-api/media/v4l/vidioc-subdev-g-frame-interval.rst b/Documentation/userspace-api/media/v4l/vidioc-subdev-g-frame-interval.rst
new file mode 100644
index 000000000..3a50f8b28
--- /dev/null
+++ b/Documentation/userspace-api/media/v4l/vidioc-subdev-g-frame-interval.rst
@@ -0,0 +1,119 @@
+.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
+.. c:namespace:: V4L
+
+.. _VIDIOC_SUBDEV_G_FRAME_INTERVAL:
+
+********************************************************************
+ioctl VIDIOC_SUBDEV_G_FRAME_INTERVAL, VIDIOC_SUBDEV_S_FRAME_INTERVAL
+********************************************************************
+
+Name
+====
+
+VIDIOC_SUBDEV_G_FRAME_INTERVAL - VIDIOC_SUBDEV_S_FRAME_INTERVAL - Get or set the frame interval on a subdev pad
+
+Synopsis
+========
+
+.. c:macro:: VIDIOC_SUBDEV_G_FRAME_INTERVAL
+
+``int ioctl(int fd, VIDIOC_SUBDEV_G_FRAME_INTERVAL, struct v4l2_subdev_frame_interval *argp)``
+
+.. c:macro:: VIDIOC_SUBDEV_S_FRAME_INTERVAL
+
+``int ioctl(int fd, VIDIOC_SUBDEV_S_FRAME_INTERVAL, struct v4l2_subdev_frame_interval *argp)``
+
+Arguments
+=========
+
+``fd``
+    File descriptor returned by :c:func:`open()`.
+
+``argp``
+    Pointer to struct :c:type:`v4l2_subdev_frame_interval`.
+
+Description
+===========
+
+These ioctls are used to get and set the frame interval at specific
+subdev pads in the image pipeline. The frame interval only makes sense
+for sub-devices that can control the frame period on their own. This
+includes, for instance, image sensors and TV tuners. Sub-devices that
+don't support frame intervals must not implement these ioctls.
+
+To retrieve the current frame interval applications set the ``pad``
+field of a struct
+:c:type:`v4l2_subdev_frame_interval` to
+the desired pad number as reported by the media controller API. When
+they call the ``VIDIOC_SUBDEV_G_FRAME_INTERVAL`` ioctl with a pointer to
+this structure the driver fills the members of the ``interval`` field.
+
+To change the current frame interval applications set both the ``pad``
+field and all members of the ``interval`` field. When they call the
+``VIDIOC_SUBDEV_S_FRAME_INTERVAL`` ioctl with a pointer to this
+structure the driver verifies the requested interval, adjusts it based
+on the hardware capabilities and configures the device. Upon return the
+struct
+:c:type:`v4l2_subdev_frame_interval`
+contains the current frame interval as would be returned by a
+``VIDIOC_SUBDEV_G_FRAME_INTERVAL`` call.
+
+Calling ``VIDIOC_SUBDEV_S_FRAME_INTERVAL`` on a subdev device node that has been
+registered in read-only mode is not allowed. An error is returned and the errno
+variable is set to ``-EPERM``.
+
+Drivers must not return an error solely because the requested interval
+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.
+
+.. c:type:: v4l2_subdev_frame_interval
+
+.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
+
+.. flat-table:: struct v4l2_subdev_frame_interval
+    :header-rows:  0
+    :stub-columns: 0
+    :widths:       1 1 2
+
+    * - __u32
+      - ``pad``
+      - Pad number as reported by the media controller API.
+    * - struct :c:type:`v4l2_fract`
+      - ``interval``
+      - Period, in seconds, between consecutive video frames.
+    * - __u32
+      - ``reserved``\ [9]
+      - Reserved for future extensions. Applications and drivers must set
+	the array to zero.
+
+Return Value
+============
+
+On success 0 is returned, on error -1 and the ``errno`` variable is set
+appropriately. The generic error codes are described at the
+:ref:`Generic Error Codes <gen-errors>` chapter.
+
+EBUSY
+    The frame interval can't be changed because the pad is currently
+    busy. This can be caused, for instance, by an active video stream on
+    the pad. The ioctl must not be retried without performing another
+    action to fix the problem first. Only returned by
+    ``VIDIOC_SUBDEV_S_FRAME_INTERVAL``
+
+EINVAL
+    The struct
+    :c:type:`v4l2_subdev_frame_interval`
+    ``pad`` references a non-existing pad, or the pad doesn't support
+    frame intervals.
+
+EPERM
+    The ``VIDIOC_SUBDEV_S_FRAME_INTERVAL`` ioctl has been called on a read-only
+    subdevice.