diff options
Diffstat (limited to 'Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst')
| -rw-r--r-- | Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst | 82 |
1 files changed, 60 insertions, 22 deletions
diff --git a/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst b/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst index b6d52083707b..daf9a6621b50 100644 --- a/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst +++ b/Documentation/userspace-api/media/v4l/vidioc-reqbufs.rst @@ -1,11 +1,5 @@ -.. 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 +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later +.. c:namespace:: V4L .. _VIDIOC_REQBUFS: @@ -18,19 +12,18 @@ Name VIDIOC_REQBUFS - Initiate Memory Mapping, User Pointer I/O or DMA buffer I/O - Synopsis ======== -.. c:function:: int ioctl( int fd, VIDIOC_REQBUFS, struct v4l2_requestbuffers *argp ) - :name: VIDIOC_REQBUFS +.. c:macro:: VIDIOC_REQBUFS +``int ioctl(int fd, VIDIOC_REQBUFS, struct v4l2_requestbuffers *argp)`` Arguments ========= ``fd`` - File descriptor returned by :ref:`open() <func-open>`. + File descriptor returned by :c:func:`open()`. ``argp`` Pointer to struct :c:type:`v4l2_requestbuffers`. @@ -76,10 +69,11 @@ 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{8.7cm}| +.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}| + +.. cssclass:: longtable .. flat-table:: struct v4l2_requestbuffers :header-rows: 0 @@ -112,12 +106,13 @@ aborting or finishing any DMA in progress, an implicit ``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. - * - __u32 - - ``reserved``\ [1] - - A place holder for future extensions. Drivers and applications - must set the array to zero. - -.. tabularcolumns:: |p{6.1cm}|p{2.2cm}|p{8.7cm}| + * - __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: @@ -126,8 +121,9 @@ aborting or finishing any DMA in progress, an implicit .. _V4L2-BUF-CAP-SUPPORTS-REQUESTS: .. _V4L2-BUF-CAP-SUPPORTS-ORPHANED-BUFS: .. _V4L2-BUF-CAP-SUPPORTS-M2M-HOLD-CAPTURE-BUF: - -.. cssclass:: longtable +.. _V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINTS: +.. _V4L2-BUF-CAP-SUPPORTS-MAX-NUM-BUFFERS: +.. _V4L2-BUF-CAP-SUPPORTS-REMOVE-BUFS: .. flat-table:: V4L2 Buffer Capabilities Flags :header-rows: 0 @@ -156,6 +152,48 @@ aborting or finishing any DMA in progress, an implicit - 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>`. + * - ``V4L2_BUF_CAP_SUPPORTS_MAX_NUM_BUFFERS`` + - 0x00000080 + - If set, then the ``max_num_buffers`` field in ``struct v4l2_create_buffers`` + is valid. If not set, then the maximum is ``VIDEO_MAX_FRAME`` buffers. + * - ``V4L2_BUF_CAP_SUPPORTS_REMOVE_BUFS`` + - 0x00000100 + - If set, then ``VIDIOC_REMOVE_BUFS`` is supported. + +.. _memory-flags: +.. _V4L2-MEMORY-FLAG-NON-COHERENT: + +.. flat-table:: Memory Consistency Flags + :header-rows: 0 + :stub-columns: 0 + :widths: 3 1 4 + + * - ``V4L2_MEMORY_FLAG_NON_COHERENT`` + - 0x00000001 + - A buffer is allocated either in coherent (it will be automatically + coherent between the CPU and the bus) or non-coherent memory. The + latter can provide performance gains, for instance the CPU cache + sync/flush operations can be avoided if the buffer is accessed by the + corresponding device only and the CPU does not read/write to/from that + buffer. However, this requires extra care from the driver -- it must + guarantee memory consistency by issuing a cache flush/sync when + consistency is needed. If this flag is set V4L2 will attempt to + allocate the buffer in non-coherent memory. The flag takes effect + only if the buffer is used for :ref:`memory mapping <mmap>` I/O and the + queue reports the :ref:`V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS + <V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINTS>` capability. + +.. raw:: latex + + \normalsize Return Value ============ |