diff options
Diffstat (limited to 'Documentation/userspace-api/media/v4l/buffer.rst')
| -rw-r--r-- | Documentation/userspace-api/media/v4l/buffer.rst | 96 |
1 files changed, 22 insertions, 74 deletions
diff --git a/Documentation/userspace-api/media/v4l/buffer.rst b/Documentation/userspace-api/media/v4l/buffer.rst index 57e752aaf414..856874341882 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: @@ -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`: @@ -596,7 +580,7 @@ Buffer Flags - ``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 @@ -615,7 +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`: @@ -687,43 +671,10 @@ Buffer Flags \normalsize -.. _memory-flags: - -Memory Consistency Flags -======================== - -.. tabularcolumns:: |p{7.0cm}|p{2.2cm}|p{8.3cm}| - -.. cssclass:: longtable - -.. flat-table:: - :header-rows: 0 - :stub-columns: 0 - :widths: 3 1 4 - - * .. _`V4L2-FLAG-MEMORY-NON-CONSISTENT`: - - - ``V4L2_FLAG_MEMORY_NON_CONSISTENT`` - - 0x00000001 - - A buffer is allocated either in consistent (it will be automatically - coherent between the CPU and the bus) or non-consistent 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-consistent 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. - -.. 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 @@ -743,7 +694,9 @@ enum v4l2_memory - 4 - The buffer is used for :ref:`DMA shared buffer <dmabuf>` I/O. +.. raw:: latex + \normalsize Timecodes ========= @@ -753,13 +706,12 @@ 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 @@ -790,14 +742,11 @@ 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 @@ -820,13 +769,12 @@ 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 |