Adding upstream version 5.10.209.upstream/5.10.209

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 165 insertions, 0 deletions

diff --git a/Documentation/userspace-api/media/v4l/field-order.rst b/Documentation/userspace-api/media/v4l/field-order.rst
new file mode 100644
index 000000000..54548ea43
--- /dev/null
+++ b/Documentation/userspace-api/media/v4l/field-order.rst
@@ -0,0 +1,165 @@
+.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
+
+.. _field-order:
+
+***********
+Field Order
+***********
+
+We have to distinguish between progressive and interlaced video.
+Progressive video transmits all lines of a video image sequentially.
+Interlaced video divides an image into two fields, containing only the
+odd and even lines of the image, respectively. Alternating the so called
+odd and even field are transmitted, and due to a small delay between
+fields a cathode ray TV displays the lines interleaved, yielding the
+original frame. This curious technique was invented because at refresh
+rates similar to film the image would fade out too quickly. Transmitting
+fields reduces the flicker without the necessity of doubling the frame
+rate and with it the bandwidth required for each channel.
+
+It is important to understand a video camera does not expose one frame
+at a time, merely transmitting the frames separated into fields. The
+fields are in fact captured at two different instances in time. An
+object on screen may well move between one field and the next. For
+applications analysing motion it is of paramount importance to recognize
+which field of a frame is older, the *temporal order*.
+
+When the driver provides or accepts images field by field rather than
+interleaved, it is also important applications understand how the fields
+combine to frames. We distinguish between top (aka odd) and bottom (aka
+even) fields, the *spatial order*: The first line of the top field is
+the first line of an interlaced frame, the first line of the bottom
+field is the second line of that frame.
+
+However because fields were captured one after the other, arguing
+whether a frame commences with the top or bottom field is pointless. Any
+two successive top and bottom, or bottom and top fields yield a valid
+frame. Only when the source was progressive to begin with, e. g. when
+transferring film to video, two fields may come from the same frame,
+creating a natural order.
+
+Counter to intuition the top field is not necessarily the older field.
+Whether the older field contains the top or bottom lines is a convention
+determined by the video standard. Hence the distinction between temporal
+and spatial order of fields. The diagrams below should make this
+clearer.
+
+In V4L it is assumed that all video cameras transmit fields on the media
+bus in the same order they were captured, so if the top field was
+captured first (is the older field), the top field is also transmitted
+first on the bus.
+
+All video capture and output devices must report the current field
+order. Some drivers may permit the selection of a different order, to
+this end applications initialize the ``field`` field of struct
+:c:type:`v4l2_pix_format` before calling the
+:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl. If this is not desired it
+should have the value ``V4L2_FIELD_ANY`` (0).
+
+
+enum v4l2_field
+===============
+
+.. c:type:: v4l2_field
+
+.. tabularcolumns:: |p{5.8cm}|p{0.6cm}|p{11.1cm}|
+
+.. cssclass:: longtable
+
+.. flat-table::
+    :header-rows:  0
+    :stub-columns: 0
+    :widths:       3 1 4
+
+    * - ``V4L2_FIELD_ANY``
+      - 0
+      - Applications request this field order when any field format
+	is acceptable. Drivers choose depending on hardware capabilities or
+	e.g. the requested image size, and return the actual field order.
+	Drivers must never return ``V4L2_FIELD_ANY``.
+	If multiple field orders are possible the
+	driver must choose one of the possible field orders during
+	:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` or
+	:ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>`. struct
+	:c:type:`v4l2_buffer` ``field`` can never be
+	``V4L2_FIELD_ANY``.
+    * - ``V4L2_FIELD_NONE``
+      - 1
+      - Images are in progressive (frame-based) format, not interlaced
+        (field-based).
+    * - ``V4L2_FIELD_TOP``
+      - 2
+      - Images consist of the top (aka odd) field only.
+    * - ``V4L2_FIELD_BOTTOM``
+      - 3
+      - Images consist of the bottom (aka even) field only. Applications
+	may wish to prevent a device from capturing interlaced images
+	because they will have "comb" or "feathering" artefacts around
+	moving objects.
+    * - ``V4L2_FIELD_INTERLACED``
+      - 4
+      - Images contain both fields, interleaved line by line. The temporal
+	order of the fields (whether the top or bottom field is older)
+	depends on the current video standard. In M/NTSC the bottom
+	field is the older field. In all other standards the top field
+	is the older field.
+    * - ``V4L2_FIELD_SEQ_TB``
+      - 5
+      - Images contain both fields, the top field lines are stored first
+	in memory, immediately followed by the bottom field lines. Fields
+	are always stored in temporal order, the older one first in
+	memory. Image sizes refer to the frame, not fields.
+    * - ``V4L2_FIELD_SEQ_BT``
+      - 6
+      - Images contain both fields, the bottom field lines are stored
+	first in memory, immediately followed by the top field lines.
+	Fields are always stored in temporal order, the older one first in
+	memory. Image sizes refer to the frame, not fields.
+    * - ``V4L2_FIELD_ALTERNATE``
+      - 7
+      - The two fields of a frame are passed in separate buffers, in
+	temporal order, i. e. the older one first. To indicate the field
+	parity (whether the current field is a top or bottom field) the
+	driver or application, depending on data direction, must set
+	struct :c:type:`v4l2_buffer` ``field`` to
+	``V4L2_FIELD_TOP`` or ``V4L2_FIELD_BOTTOM``. Any two successive
+	fields pair to build a frame. If fields are successive, without
+	any dropped fields between them (fields can drop individually),
+	can be determined from the struct
+	:c:type:`v4l2_buffer` ``sequence`` field. This
+	format cannot be selected when using the read/write I/O method
+	since there is no way to communicate if a field was a top or
+	bottom field.
+    * - ``V4L2_FIELD_INTERLACED_TB``
+      - 8
+      - Images contain both fields, interleaved line by line, top field
+	first. The top field is the older field.
+    * - ``V4L2_FIELD_INTERLACED_BT``
+      - 9
+      - Images contain both fields, interleaved line by line, top field
+	first. The bottom field is the older field.
+
+
+
+.. _fieldseq-tb:
+
+Field Order, Top Field First Transmitted
+========================================
+
+.. kernel-figure:: fieldseq_tb.svg
+    :alt:    fieldseq_tb.svg
+    :align:  center
+
+    Field Order, Top Field First Transmitted
+
+
+.. _fieldseq-bt:
+
+Field Order, Bottom Field First Transmitted
+===========================================
+
+.. kernel-figure:: fieldseq_bt.svg
+    :alt:    fieldseq_bt.svg
+    :align:  center
+
+    Field Order, Bottom Field First Transmitted