1 files changed, 68 insertions, 0 deletions
diff --git a/Documentation/userspace-api/media/v4l/planar-apis.rst b/Documentation/userspace-api/media/v4l/planar-apis.rst
new file mode 100644
index 000000000000..6247b0c4ab4d
--- /dev/null
+++ b/Documentation/userspace-api/media/v4l/planar-apis.rst
@@ -0,0 +1,68 @@
+.. Permission is granted to copy, distribute and/or modify this
+.. document under the terms of the GNU Free Documentation License,
+.. Version 1.1 or any later version published by the Free Software
+.. Foundation, with no Invariant Sections, no Front-Cover Texts
+.. and no Back-Cover Texts. A copy of the license is included at
+.. Documentation/userspace-api/media/fdl-appendix.rst.
+..
+.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
+
+.. _planar-apis:
+
+*****************************
+Single- and multi-planar APIs
+*****************************
+
+Some devices require data for each input or output video frame to be
+placed in discontiguous memory buffers. In such cases, one video frame
+has to be addressed using more than one memory address, i.e. one pointer
+per "plane". A plane is a sub-buffer of the current frame. For examples
+of such formats see :ref:`pixfmt`.
+
+Initially, V4L2 API did not support multi-planar buffers and a set of
+extensions has been introduced to handle them. Those extensions
+constitute what is being referred to as the "multi-planar API".
+
+Some of the V4L2 API calls and structures are interpreted differently,
+depending on whether single- or multi-planar API is being used. An
+application can choose whether to use one or the other by passing a
+corresponding buffer type to its ioctl calls. Multi-planar versions of
+buffer types are suffixed with an ``_MPLANE`` string. For a list of
+available multi-planar buffer types see enum
+:c:type:`v4l2_buf_type`.
+
+
+Multi-planar formats
+====================
+
+Multi-planar API introduces new multi-planar formats. Those formats use
+a separate set of FourCC codes. It is important to distinguish between
+the multi-planar API and a multi-planar format. Multi-planar API calls
+can handle all single-planar formats as well (as long as they are passed
+in multi-planar API structures), while the single-planar API cannot
+handle multi-planar formats.
+
+
+Calls that distinguish between single and multi-planar APIs
+===========================================================
+
+:ref:`VIDIOC_QUERYCAP <VIDIOC_QUERYCAP>`
+    Two additional multi-planar capabilities are added. They can be set
+    together with non-multi-planar ones for devices that handle both
+    single- and multi-planar formats.
+
+:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>`, :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`, :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>`
+    New structures for describing multi-planar formats are added: struct
+    :c:type:`v4l2_pix_format_mplane` and
+    struct :c:type:`v4l2_plane_pix_format`.
+    Drivers may define new multi-planar formats, which have distinct
+    FourCC codes from the existing single-planar ones.
+
+:ref:`VIDIOC_QBUF <VIDIOC_QBUF>`, :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>`, :ref:`VIDIOC_QUERYBUF <VIDIOC_QUERYBUF>`
+    A new struct :c:type:`v4l2_plane` structure for
+    describing planes is added. Arrays of this structure are passed in
+    the new ``m.planes`` field of struct
+    :c:type:`v4l2_buffer`.
+
+:ref:`VIDIOC_REQBUFS <VIDIOC_REQBUFS>`
+    Will allocate multi-planar buffers as requested.