[PATCH 1/1] v4l: Add note on buffer locking to memory and DMA mapping to PREPARE_BUF

[Sakari Ailus <sakari.ailus@iki.fi>]

Add note to documentation of VIDIOC_PREPARE_BUF that the preparation done by
the IOCTL may include locking buffers to system memory and creating DMA
mappings for them.

Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
---
 .../DocBook/media/v4l/vidioc-prepare-buf.xml       |    8 +++++---
 1 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/Documentation/DocBook/media/v4l/vidioc-prepare-buf.xml b/Documentation/DocBook/media/v4l/vidioc-prepare-buf.xml
index 509e752..7177c2f 100644
--- a/Documentation/DocBook/media/v4l/vidioc-prepare-buf.xml
+++ b/Documentation/DocBook/media/v4l/vidioc-prepare-buf.xml
@@ -52,9 +52,11 @@
 <constant>VIDIOC_PREPARE_BUF</constant> ioctl to pass ownership of the buffer
 to the driver before actually enqueuing it, using the
 <constant>VIDIOC_QBUF</constant> ioctl, and to prepare it for future I/O.
-Such preparations may include cache invalidation or cleaning. Performing them
-in advance saves time during the actual I/O. In case such cache operations are
-not required, the application can use one of
+Such preparations may include locking the buffer to system memory and
+creating DMA mapping for it (on the first time
+<constant>VIDIOC_PREPARE_BUF</constant> is called), cache invalidation or
+cleaning. Performing them in advance saves time during the actual I/O. In
+case such cache operations are not required, the application can use one of
 <constant>V4L2_BUF_FLAG_NO_CACHE_INVALIDATE</constant> and
 <constant>V4L2_BUF_FLAG_NO_CACHE_CLEAN</constant> flags to skip the respective
 step.</para>
-- 
1.7.2.5