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Diffstat (limited to 'Documentation/userspace-api/media/v4l/buffer.rst')
| -rw-r--r-- | Documentation/userspace-api/media/v4l/buffer.rst | 82 |
1 files changed, 34 insertions, 48 deletions
diff --git a/Documentation/userspace-api/media/v4l/buffer.rst b/Documentation/userspace-api/media/v4l/buffer.rst index 951ae1ed485f..94dc2719e907 100644 --- a/Documentation/userspace-api/media/v4l/buffer.rst +++ b/Documentation/userspace-api/media/v4l/buffer.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 .. _buffer: @@ -23,8 +17,8 @@ argument to the :ref:`VIDIOC_QUERYBUF`, :ref:`VIDIOC_QBUF <VIDIOC_QBUF>` and :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl. In the multi-planar API, some plane-specific members of struct :c:type:`v4l2_buffer`, -such as pointers and sizes for each plane, are stored in struct -struct :c:type:`v4l2_plane` instead. In that case, struct +such as pointers and sizes for each plane, are stored in +struct :c:type:`v4l2_plane` instead. In that case, struct :c:type:`v4l2_buffer` contains an array of plane structures. Dequeued video buffers come with timestamps. The driver decides at which @@ -40,7 +34,6 @@ mem-to-mem devices is an exception to the rule: the timestamp source flags are copied from the OUTPUT video buffer to the CAPTURE video buffer. - Interactions between formats, controls and buffers ================================================== @@ -159,13 +152,12 @@ based on the queried sizes (for instance by allocating a set of buffers large enough for all the desired formats and controls, or by allocating separate set of appropriately sized buffers for each use case). - .. c:type:: v4l2_buffer struct v4l2_buffer ================== -.. tabularcolumns:: |p{2.8cm}|p{2.5cm}|p{1.6cm}|p{10.2cm}| +.. tabularcolumns:: |p{2.9cm}|p{2.4cm}|p{12.0cm}| .. cssclass:: longtable @@ -195,10 +187,8 @@ struct v4l2_buffer on the negotiated data format and may change with each buffer for compressed variable size data like JPEG images. Drivers must set this field when ``type`` refers to a capture stream, applications - when it refers to an output stream. If the application sets this - to 0 for an output stream, then ``bytesused`` will be set to the - size of the buffer (see the ``length`` field of this struct) by - the driver. For multiplanar formats this field is ignored and the + when it refers to an output stream. For multiplanar formats this field + is ignored and the ``planes`` pointer is used instead. * - __u32 - ``flags`` @@ -264,7 +254,7 @@ struct v4l2_buffer ``V4L2_MEMORY_MMAP`` this is the offset of the buffer from the start of the device memory. The value is returned by the driver and apart of serving as parameter to the - :ref:`mmap() <func-mmap>` function not useful for applications. + :c:func:`mmap()` function not useful for applications. See :ref:`mmap` for details * - unsigned long - ``userptr`` @@ -317,13 +307,12 @@ struct v4l2_buffer given, then ``EINVAL`` will be returned. - .. c:type:: v4l2_plane struct v4l2_plane ================= -.. tabularcolumns:: |p{3.5cm}|p{3.5cm}|p{3.5cm}|p{7.0cm}| +.. tabularcolumns:: |p{3.5cm}|p{3.5cm}|p{10.3cm}| .. cssclass:: longtable @@ -336,10 +325,7 @@ struct v4l2_plane - ``bytesused`` - The number of bytes occupied by data in the plane (its payload). Drivers must set this field when ``type`` refers to a capture - stream, applications when it refers to an output stream. If the - application sets this to 0 for an output stream, then - ``bytesused`` will be set to the size of the plane (see the - ``length`` field of this struct) by the driver. + stream, applications when it refers to an output stream. .. note:: @@ -357,7 +343,7 @@ struct v4l2_plane - ``mem_offset`` - When the memory type in the containing struct :c:type:`v4l2_buffer` is ``V4L2_MEMORY_MMAP``, this - is the value that should be passed to :ref:`mmap() <func-mmap>`, + is the value that should be passed to :c:func:`mmap()`, similar to the ``offset`` field in struct :c:type:`v4l2_buffer`. * - unsigned long @@ -391,7 +377,6 @@ struct v4l2_plane applications. - .. c:type:: v4l2_buf_type enum v4l2_buf_type @@ -399,7 +384,7 @@ enum v4l2_buf_type .. cssclass:: longtable -.. tabularcolumns:: |p{7.8cm}|p{0.6cm}|p{9.1cm}| +.. tabularcolumns:: |p{7.8cm}|p{0.6cm}|p{8.9cm}| .. flat-table:: :header-rows: 0 @@ -455,7 +440,6 @@ enum v4l2_buf_type - Buffer for metadata output, see :ref:`metadata`. - .. _buffer-flags: Buffer Flags @@ -463,16 +447,16 @@ Buffer Flags .. raw:: latex - \small + \footnotesize -.. tabularcolumns:: |p{7.0cm}|p{2.1cm}|p{8.4cm}| +.. tabularcolumns:: |p{6.5cm}|p{1.8cm}|p{9.0cm}| .. cssclass:: longtable .. flat-table:: :header-rows: 0 :stub-columns: 0 - :widths: 3 1 4 + :widths: 65 18 70 * .. _`V4L2-BUF-FLAG-MAPPED`: @@ -565,9 +549,9 @@ Buffer Flags - 0x00000400 - The buffer has been prepared for I/O and can be queued by the application. Drivers set or clear this flag when the - :ref:`VIDIOC_QUERYBUF`, + :ref:`VIDIOC_QUERYBUF <VIDIOC_QUERYBUF>`, :ref:`VIDIOC_PREPARE_BUF <VIDIOC_QBUF>`, - :ref:`VIDIOC_QBUF` or + :ref:`VIDIOC_QBUF <VIDIOC_QBUF>` or :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl is called. * .. _`V4L2-BUF-FLAG-NO-CACHE-INVALIDATE`: @@ -577,7 +561,10 @@ Buffer Flags applications shall use this flag if the data captured in the buffer is not going to be touched by the CPU, instead the buffer will, probably, be passed on to a DMA-capable hardware unit for - further processing or output. + further processing or output. This flag is ignored unless the + queue is used for :ref:`memory mapping <mmap>` streaming I/O and + reports :ref:`V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS + <V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINTS>` capability. * .. _`V4L2-BUF-FLAG-NO-CACHE-CLEAN`: - ``V4L2_BUF_FLAG_NO_CACHE_CLEAN`` @@ -585,12 +572,15 @@ Buffer Flags - Caches do not have to be cleaned for this buffer. Typically applications shall use this flag for output buffers if the data in this buffer has not been created by the CPU but by some - DMA-capable unit, in which case caches have not been used. + DMA-capable unit, in which case caches have not been used. This flag + is ignored unless the queue is used for :ref:`memory mapping <mmap>` + streaming I/O and reports :ref:`V4L2_BUF_CAP_SUPPORTS_MMAP_CACHE_HINTS + <V4L2-BUF-CAP-SUPPORTS-MMAP-CACHE-HINTS>` capability. * .. _`V4L2-BUF-FLAG-M2M-HOLD-CAPTURE-BUF`: - ``V4L2_BUF_FLAG_M2M_HOLD_CAPTURE_BUF`` - 0x00000200 - - Only valid if ``V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF`` is + - Only valid if struct :c:type:`v4l2_requestbuffers` flag ``V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF`` is set. It is typically used with stateless decoders where multiple output buffers each decode to a slice of the decoded frame. Applications can set this flag when queueing the output buffer @@ -609,7 +599,7 @@ Buffer Flags :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl is called. Due to hardware limitations, the last buffer may be empty. In this case the driver will set the ``bytesused`` field to 0, regardless of - the format. Any Any subsequent call to the + the format. Any subsequent call to the :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` ioctl will not block anymore, but return an ``EPIPE`` error code. * .. _`V4L2-BUF-FLAG-REQUEST-FD`: @@ -677,17 +667,16 @@ Buffer Flags exposure of the frame has begun. This is only valid for the ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` buffer type. +.. c:enum:: v4l2_memory + .. raw:: latex \normalsize - -.. c:type:: v4l2_memory - enum v4l2_memory ================ -.. tabularcolumns:: |p{5.0cm}|p{0.8cm}|p{11.7cm}| +.. tabularcolumns:: |p{5.0cm}|p{0.8cm}|p{11.5cm}| .. flat-table:: :header-rows: 0 @@ -707,7 +696,9 @@ enum v4l2_memory - 4 - The buffer is used for :ref:`DMA shared buffer <dmabuf>` I/O. +.. raw:: latex + \normalsize Timecodes ========= @@ -717,13 +708,12 @@ The :c:type:`v4l2_buffer_timecode` structure is designed to hold a (struct :c:type:`timeval` timestamps are stored in the struct :c:type:`v4l2_buffer` ``timestamp`` field.) - .. c:type:: v4l2_timecode struct v4l2_timecode -------------------- -.. tabularcolumns:: |p{1.4cm}|p{2.8cm}|p{12.3cm}| +.. tabularcolumns:: |p{1.4cm}|p{2.8cm}|p{13.1cm}| .. flat-table:: :header-rows: 0 @@ -754,14 +744,11 @@ struct v4l2_timecode - The "user group" bits from the timecode. - .. _timecode-type: Timecode Types -------------- -.. tabularcolumns:: |p{5.6cm}|p{0.8cm}|p{11.1cm}| - .. flat-table:: :header-rows: 0 :stub-columns: 0 @@ -784,13 +771,12 @@ Timecode Types - - .. _timecode-flags: Timecode Flags -------------- -.. tabularcolumns:: |p{6.6cm}|p{1.4cm}|p{9.5cm}| +.. tabularcolumns:: |p{6.6cm}|p{1.4cm}|p{9.3cm}| .. flat-table:: :header-rows: 0 |