media: docs: move uAPI book to userspace-api/media

Since 2017, there is an space reserved for userspace API,
created by changeset 1d596dee3862 ("docs: Create a user-space API guide").

As the media subsystem was one of the first subsystems to use
Sphinx, until this patch, we were keeping things on a separate
place.

Let's just use the new location, as having all uAPI altogether
will likely make things easier for developers.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

1 files changed, 67 insertions, 0 deletions

diff --git a/Documentation/userspace-api/media/v4l/pixfmt-nv12mt.rst b/Documentation/userspace-api/media/v4l/pixfmt-nv12mt.rst
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+.. 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
+
+.. _V4L2-PIX-FMT-NV12MT:
+
+****************************
+V4L2_PIX_FMT_NV12MT ('TM12')
+****************************
+
+Formats with ½ horizontal and vertical chroma resolution. This format
+has two planes - one for luminance and one for chrominance. Chroma
+samples are interleaved. The difference to ``V4L2_PIX_FMT_NV12`` is the
+memory layout. Pixels are grouped in macroblocks of 64x32 size. The
+order of macroblocks in memory is also not standard.
+
+
+Description
+===========
+
+This is the two-plane versions of the YUV 4:2:0 format where data is
+grouped into 64x32 macroblocks. The three components are separated into
+two sub-images or planes. The Y plane has one byte per pixel and pixels
+are grouped into 64x32 macroblocks. The CbCr plane has the same width,
+in bytes, as the Y plane (and the image), but is half as tall in pixels.
+The chroma plane is also grouped into 64x32 macroblocks.
+
+Width of the buffer has to be aligned to the multiple of 128, and height
+alignment is 32. Every four adjacent buffers - two horizontally and two
+vertically are grouped together and are located in memory in Z or
+flipped Z order.
+
+Layout of macroblocks in memory is presented in the following figure.
+
+
+.. _nv12mt:
+
+.. kernel-figure:: nv12mt.svg
+    :alt:    nv12mt.svg
+    :align:  center
+
+    V4L2_PIX_FMT_NV12MT macroblock Z shape memory layout
+
+The requirement that width is multiple of 128 is implemented because,
+the Z shape cannot be cut in half horizontally. In case the vertical
+resolution of macroblocks is odd then the last row of macroblocks is
+arranged in a linear order.
+
+In case of chroma the layout is identical. Cb and Cr samples are
+interleaved. Height of the buffer is aligned to 32.
+
+
+.. _nv12mt_ex:
+
+.. kernel-figure:: nv12mt_example.svg
+    :alt:    nv12mt_example.svg
+    :align:  center
+
+    Example V4L2_PIX_FMT_NV12MT memory layout of macroblocks
+
+Memory layout of macroblocks of ``V4L2_PIX_FMT_NV12MT`` format in most
+extreme case.