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Diffstat (limited to 'Documentation/userspace-api/media/v4l/mmap.rst')
| -rw-r--r-- | Documentation/userspace-api/media/v4l/mmap.rst | 26 |
1 files changed, 13 insertions, 13 deletions
diff --git a/Documentation/userspace-api/media/v4l/mmap.rst b/Documentation/userspace-api/media/v4l/mmap.rst index 1cce31c6de79..16b1e13b029f 100644 --- a/Documentation/userspace-api/media/v4l/mmap.rst +++ b/Documentation/userspace-api/media/v4l/mmap.rst @@ -1,4 +1,5 @@ .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later +.. c:namespace:: V4L .. _mmap: @@ -35,22 +36,22 @@ This ioctl can also be used to change the number of buffers or to free the allocated memory, provided none of the buffers are still mapped. Before applications can access the buffers they must map them into their -address space with the :ref:`mmap() <func-mmap>` function. The +address space with the :c:func:`mmap()` function. The location of the buffers in device memory can be determined with the :ref:`VIDIOC_QUERYBUF` ioctl. In the single-planar API case, the ``m.offset`` and ``length`` returned in a struct :c:type:`v4l2_buffer` are passed as sixth and second -parameter to the :ref:`mmap() <func-mmap>` function. When using the +parameter to the :c:func:`mmap()` function. When using the multi-planar API, struct :c:type:`v4l2_buffer` contains an array of struct :c:type:`v4l2_plane` structures, each containing its own ``m.offset`` and ``length``. When using the multi-planar API, every plane of every buffer has to be mapped -separately, so the number of calls to :ref:`mmap() <func-mmap>` should +separately, so the number of calls to :c:func:`mmap()` should be equal to number of buffers times number of planes in each buffer. The offset and length values must not be modified. Remember, the buffers are allocated in physical memory, as opposed to virtual memory, which can be swapped out to disk. Applications should free the buffers as soon as -possible with the :ref:`munmap() <func-munmap>` function. +possible with the :c:func:`munmap()` function. Example: Mapping buffers in the single-planar API ================================================= @@ -122,7 +123,6 @@ Example: Mapping buffers in the single-planar API for (i = 0; i < reqbuf.count; i++) munmap(buffers[i].start, buffers[i].length); - Example: Mapping buffers in the multi-planar API ================================================ @@ -238,10 +238,10 @@ be determined at any time using the :ref:`VIDIOC_QUERYBUF` ioctl. Two methods exist to suspend execution of the application until one or more buffers can be dequeued. By default :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` blocks when no buffer is in the outgoing queue. When the ``O_NONBLOCK`` -flag was given to the :ref:`open() <func-open>` function, +flag was given to the :c:func:`open()` function, :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` returns immediately with an ``EAGAIN`` -error code when no buffer is available. The :ref:`select() <func-select>` -or :ref:`poll() <func-poll>` functions are always available. +error code when no buffer is available. The :c:func:`select()` +or :c:func:`poll()` functions are always available. To start and stop capturing or output applications call the :ref:`VIDIOC_STREAMON <VIDIOC_STREAMON>` and :ref:`VIDIOC_STREAMOFF @@ -259,15 +259,15 @@ Drivers implementing memory mapping I/O must support the <VIDIOC_QUERYBUF>`, :ref:`VIDIOC_QBUF <VIDIOC_QBUF>`, :ref:`VIDIOC_DQBUF <VIDIOC_QBUF>`, :ref:`VIDIOC_STREAMON <VIDIOC_STREAMON>` and :ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>` ioctls, the :ref:`mmap() -<func-mmap>`, :ref:`munmap() <func-munmap>`, :ref:`select() -<func-select>` and :ref:`poll() <func-poll>` function. [#f3]_ +<func-mmap>`, :c:func:`munmap()`, :ref:`select() +<func-select>` and :c:func:`poll()` function. [#f3]_ [capture example] .. [#f1] One could use one file descriptor and set the buffer type field accordingly when calling :ref:`VIDIOC_QBUF` etc., - but it makes the :ref:`select() <func-select>` function ambiguous. We also + but it makes the :c:func:`select()` function ambiguous. We also like the clean approach of one file descriptor per logical stream. Video overlay for example is also a logical stream, although the CPU is not needed for continuous operation. @@ -280,6 +280,6 @@ and :ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>` ioctls, the :ref:`mmap() scatter-gather lists and the like. .. [#f3] - At the driver level :ref:`select() <func-select>` and :ref:`poll() <func-poll>` are - the same, and :ref:`select() <func-select>` is too important to be optional. + At the driver level :c:func:`select()` and :c:func:`poll()` are + the same, and :c:func:`select()` is too important to be optional. The rest should be evident. |