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Diffstat (limited to 'Documentation/userspace-api/media/v4l/buffer.rst')
| -rw-r--r-- | Documentation/userspace-api/media/v4l/buffer.rst | 40 |
1 files changed, 38 insertions, 2 deletions
diff --git a/Documentation/userspace-api/media/v4l/buffer.rst b/Documentation/userspace-api/media/v4l/buffer.rst index e991ba73d873..4638ec64db00 100644 --- a/Documentation/userspace-api/media/v4l/buffer.rst +++ b/Documentation/userspace-api/media/v4l/buffer.rst @@ -676,8 +676,6 @@ Buffer Flags \normalsize -.. _memory-flags: - enum v4l2_memory ================ @@ -701,6 +699,44 @@ enum v4l2_memory - 4 - The buffer is used for :ref:`DMA shared buffer <dmabuf>` I/O. +.. _memory-flags: + +Memory Consistency Flags +------------------------ + +.. raw:: latex + + \small + +.. tabularcolumns:: |p{7.0cm}|p{2.1cm}|p{8.4cm}| + +.. cssclass:: longtable + +.. flat-table:: + :header-rows: 0 + :stub-columns: 0 + :widths: 3 1 4 + + * .. _`V4L2-MEMORY-FLAG-NON-COHERENT`: + + - ``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 Timecodes ========= |