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-rw-r--r--Documentation/userspace-api/media/v4l/buffer.rst40
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
=========