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>
diff --git a/Documentation/userspace-api/media/v4l/dev-osd.rst b/Documentation/userspace-api/media/v4l/dev-osd.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
+
+.. _osd:
+
+******************************
+Video Output Overlay Interface
+******************************
+
+**Also known as On-Screen Display (OSD)**
+
+Some video output devices can overlay a framebuffer image onto the
+outgoing video signal. Applications can set up such an overlay using
+this interface, which borrows structures and ioctls of the
+:ref:`Video Overlay <overlay>` interface.
+
+The OSD function is accessible through the same character special file
+as the :ref:`Video Output <capture>` function.
+
+.. note::
+
+ The default function of such a ``/dev/video`` device is video
+ capturing or output. The OSD function is only available after calling
+ the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl.
+
+
+Querying Capabilities
+=====================
+
+Devices supporting the *Video Output Overlay* interface set the
+``V4L2_CAP_VIDEO_OUTPUT_OVERLAY`` flag in the ``capabilities`` field of
+struct :c:type:`v4l2_capability` returned by the
+:ref:`VIDIOC_QUERYCAP` ioctl.
+
+
+Framebuffer
+===========
+
+Contrary to the *Video Overlay* interface the framebuffer is normally
+implemented on the TV card and not the graphics card. On Linux it is
+accessible as a framebuffer device (``/dev/fbN``). Given a V4L2 device,
+applications can find the corresponding framebuffer device by calling
+the :ref:`VIDIOC_G_FBUF <VIDIOC_G_FBUF>` ioctl. It returns, amongst
+other information, the physical address of the framebuffer in the
+``base`` field of struct :c:type:`v4l2_framebuffer`.
+The framebuffer device ioctl ``FBIOGET_FSCREENINFO`` returns the same
+address in the ``smem_start`` field of struct
+struct :c:type:`fb_fix_screeninfo`. The ``FBIOGET_FSCREENINFO``
+ioctl and struct :c:type:`fb_fix_screeninfo` are defined in
+the ``linux/fb.h`` header file.
+
+The width and height of the framebuffer depends on the current video
+standard. A V4L2 driver may reject attempts to change the video standard
+(or any other ioctl which would imply a framebuffer size change) with an
+``EBUSY`` error code until all applications closed the framebuffer device.
+
+Example: Finding a framebuffer device for OSD
+---------------------------------------------
+
+.. code-block:: c
+
+ #include <linux/fb.h>
+
+ struct v4l2_framebuffer fbuf;
+ unsigned int i;
+ int fb_fd;
+
+ if (-1 == ioctl(fd, VIDIOC_G_FBUF, &fbuf)) {
+ perror("VIDIOC_G_FBUF");
+ exit(EXIT_FAILURE);
+ }
+
+ for (i = 0; i < 30; i++) {
+ char dev_name[16];
+ struct fb_fix_screeninfo si;
+
+ snprintf(dev_name, sizeof(dev_name), "/dev/fb%u", i);
+
+ fb_fd = open(dev_name, O_RDWR);
+ if (-1 == fb_fd) {
+ switch (errno) {
+ case ENOENT: /* no such file */
+ case ENXIO: /* no driver */
+ continue;
+
+ default:
+ perror("open");
+ exit(EXIT_FAILURE);
+ }
+ }
+
+ if (0 == ioctl(fb_fd, FBIOGET_FSCREENINFO, &si)) {
+ if (si.smem_start == (unsigned long)fbuf.base)
+ break;
+ } else {
+ /* Apparently not a framebuffer device. */
+ }
+
+ close(fb_fd);
+ fb_fd = -1;
+ }
+
+ /* fb_fd is the file descriptor of the framebuffer device
+ for the video output overlay, or -1 if no device was found. */
+
+
+Overlay Window and Scaling
+==========================
+
+The overlay is controlled by source and target rectangles. The source
+rectangle selects a subsection of the framebuffer image to be overlaid,
+the target rectangle an area in the outgoing video signal where the
+image will appear. Drivers may or may not support scaling, and arbitrary
+sizes and positions of these rectangles. Further drivers may support any
+(or none) of the clipping/blending methods defined for the
+:ref:`Video Overlay <overlay>` interface.
+
+A struct :c:type:`v4l2_window` defines the size of the
+source rectangle, its position in the framebuffer and the
+clipping/blending method to be used for the overlay. To get the current
+parameters applications set the ``type`` field of a struct
+:c:type:`v4l2_format` to
+``V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY`` and call the
+:ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` ioctl. The driver fills the
+struct :c:type:`v4l2_window` substructure named ``win``. It is not
+possible to retrieve a previously programmed clipping list or bitmap.
+
+To program the source rectangle applications set the ``type`` field of a
+struct :c:type:`v4l2_format` to
+``V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY``, initialize the ``win``
+substructure and call the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl.
+The driver adjusts the parameters against hardware limits and returns
+the actual parameters as :ref:`VIDIOC_G_FMT <VIDIOC_G_FMT>` does. Like :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>`,
+the :ref:`VIDIOC_TRY_FMT <VIDIOC_G_FMT>` ioctl can be used to learn
+about driver capabilities without actually changing driver state. Unlike
+:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` this also works after the overlay has been enabled.
+
+A struct :c:type:`v4l2_crop` defines the size and position
+of the target rectangle. The scaling factor of the overlay is implied by
+the width and height given in struct :c:type:`v4l2_window`
+and struct :c:type:`v4l2_crop`. The cropping API applies to
+*Video Output* and *Video Output Overlay* devices in the same way as to
+*Video Capture* and *Video Overlay* devices, merely reversing the
+direction of the data flow. For more information see :ref:`crop`.
+
+
+Enabling Overlay
+================
+
+There is no V4L2 ioctl to enable or disable the overlay, however the
+framebuffer interface of the driver may support the ``FBIOBLANK`` ioctl.
