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diff --git a/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst b/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst new file mode 100644 index 000000000..099fa6695 --- /dev/null +++ b/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst @@ -0,0 +1,181 @@ +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later +.. c:namespace:: V4L + +.. _VIDIOC_REQBUFS: + +******************** +ioctl VIDIOC_REQBUFS +******************** + +Name +==== + +VIDIOC_REQBUFS - Initiate Memory Mapping, User Pointer I/O or DMA buffer I/O + +Synopsis +======== + +.. c:macro:: VIDIOC_REQBUFS + +``int ioctl(int fd, VIDIOC_REQBUFS, struct v4l2_requestbuffers *argp)`` + +Arguments +========= + +``fd`` + File descriptor returned by :c:func:`open()`. + +``argp`` + Pointer to struct :c:type:`v4l2_requestbuffers`. + +Description +=========== + +This ioctl is used to initiate :ref:`memory mapped <mmap>`, +:ref:`user pointer <userp>` or :ref:`DMABUF <dmabuf>` based I/O. +Memory mapped buffers are located in device memory and must be allocated +with this ioctl before they can be mapped into the application's address +space. User buffers are allocated by applications themselves, and this +ioctl is merely used to switch the driver into user pointer I/O mode and +to setup some internal structures. Similarly, DMABUF buffers are +allocated by applications through a device driver, and this ioctl only +configures the driver into DMABUF I/O mode without performing any direct +allocation. + +To allocate device buffers applications initialize all fields of the +struct :c:type:`v4l2_requestbuffers` structure. They set the ``type`` +field to the respective stream or buffer type, the ``count`` field to +the desired number of buffers, ``memory`` must be set to the requested +I/O method and the ``reserved`` array must be zeroed. When the ioctl is +called with a pointer to this structure the driver will attempt to +allocate the requested number of buffers and it stores the actual number +allocated in the ``count`` field. It can be smaller than the number +requested, even zero, when the driver runs out of free memory. A larger +number is also possible when the driver requires more buffers to +function correctly. For example video output requires at least two +buffers, one displayed and one filled by the application. + +When the I/O method is not supported the ioctl returns an ``EINVAL`` error +code. + +Applications can call :ref:`VIDIOC_REQBUFS` again to change the number of +buffers. Note that if any buffers are still mapped or exported via DMABUF, +then :ref:`VIDIOC_REQBUFS` can only succeed if the +``V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS`` capability is set. Otherwise +:ref:`VIDIOC_REQBUFS` will return the ``EBUSY`` error code. +If ``V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS`` is set, then these buffers are +orphaned and will be freed when they are unmapped or when the exported DMABUF +fds are closed. A ``count`` value of zero frees or orphans all buffers, after +aborting or finishing any DMA in progress, an implicit +:ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>`. + +.. c:type:: v4l2_requestbuffers + +.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}| + +.. flat-table:: struct v4l2_requestbuffers + :header-rows: 0 + :stub-columns: 0 + :widths: 1 1 2 + + * - __u32 + - ``count`` + - The number of buffers requested or granted. + * - __u32 + - ``type`` + - Type of the stream or buffers, this is the same as the struct + :c:type:`v4l2_format` ``type`` field. See + :c:type:`v4l2_buf_type` for valid values. + * - __u32 + - ``memory`` + - Applications set this field to ``V4L2_MEMORY_MMAP``, + ``V4L2_MEMORY_DMABUF`` or ``V4L2_MEMORY_USERPTR``. See + :c:type:`v4l2_memory`. + * - __u32 + - ``capabilities`` + - Set by the driver. If 0, then the driver doesn't support + capabilities. In that case all you know is that the driver is + guaranteed to support ``V4L2_MEMORY_MMAP`` and *might* support + other :c:type:`v4l2_memory` types. It will not support any other + capabilities. + + If you want to query the capabilities with a minimum of side-effects, + then this can be called with ``count`` set to 0, ``memory`` set to + ``V4L2_MEMORY_MMAP`` and ``type`` set to the buffer type. This will + free any previously allocated buffers, so this is typically something + that will be done at the start of the application. + * - __u8 + - ``flags`` + - Specifies additional buffer management attributes. + See :ref:`memory-flags`. + * - __u8 + - ``reserved``\ [3] + - Reserved for future extensions. + +.. _v4l2-buf-capabilities: +.. _V4L2-BUF-CAP-SUPPORTS-MMAP: +.. _V4L2-BUF-CAP-SUPPORTS-USERPTR: +.. _V4L2-BUF-CAP-SUPPORTS-DMABUF: +.. _V4L2-BUF-CAP-SUPPORTS-REQUESTS: +.. _V4L2-BUF-CAP-SUPPORTS-ORPHANED-BUFS: +.. _V4L2-BUF-CAP-SUPPORTS-M2M-HOLD-CAPTURE-BUF: +.. _V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINTS: + +.. raw:: latex + + \footnotesize + +.. tabularcolumns:: |p{8.1cm}|p{2.2cm}|p{7.0cm}| + +.. cssclass:: longtable + +.. flat-table:: V4L2 Buffer Capabilities Flags + :header-rows: 0 + :stub-columns: 0 + :widths: 3 1 4 + + * - ``V4L2_BUF_CAP_SUPPORTS_MMAP`` + - 0x00000001 + - This buffer type supports the ``V4L2_MEMORY_MMAP`` streaming mode. + * - ``V4L2_BUF_CAP_SUPPORTS_USERPTR`` + - 0x00000002 + - This buffer type supports the ``V4L2_MEMORY_USERPTR`` streaming mode. + * - ``V4L2_BUF_CAP_SUPPORTS_DMABUF`` + - 0x00000004 + - This buffer type supports the ``V4L2_MEMORY_DMABUF`` streaming mode. + * - ``V4L2_BUF_CAP_SUPPORTS_REQUESTS`` + - 0x00000008 + - This buffer type supports :ref:`requests <media-request-api>`. + * - ``V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS`` + - 0x00000010 + - The kernel allows calling :ref:`VIDIOC_REQBUFS` while buffers are still + mapped or exported via DMABUF. These orphaned buffers will be freed + when they are unmapped or when the exported DMABUF fds are closed. + * - ``V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF`` + - 0x00000020 + - Only valid for stateless decoders. If set, then userspace can set the + ``V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF`` flag to hold off on returning the + capture buffer until the OUTPUT timestamp changes. + * - ``V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS`` + - 0x00000040 + - This capability is set by the driver to indicate that the queue supports + cache and memory management hints. However, it's only valid when the + queue is used for :ref:`memory mapping <mmap>` streaming I/O. See + :ref:`V4L2_BUF_FLAG_NO_CACHE_INVALIDATE <V4L2-BUF-FLAG-NO-CACHE-INVALIDATE>`, + :ref:`V4L2_BUF_FLAG_NO_CACHE_CLEAN <V4L2-BUF-FLAG-NO-CACHE-CLEAN>` and + :ref:`V4L2_MEMORY_FLAG_NON_COHERENT <V4L2-MEMORY-FLAG-NON-COHERENT>`. + +.. raw:: latex + + \normalsize + +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. + +EINVAL + The buffer type (``type`` field) or the requested I/O method + (``memory``) is not supported. |