[PATCH v8 2/6] V4L: File handles: Add documentation

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Add documentation on using V4L2 file handles (v4l2_fh) in V4L2 drivers.

Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxxxxxxxxxxxxx>
---
 Documentation/video4linux/v4l2-framework.txt |   37 ++++++++++++++++++++++++++
 1 files changed, 37 insertions(+), 0 deletions(-)

diff --git a/Documentation/video4linux/v4l2-framework.txt b/Documentation/video4linux/v4l2-framework.txt
index 74d677c..bfaf0c5 100644
--- a/Documentation/video4linux/v4l2-framework.txt
+++ b/Documentation/video4linux/v4l2-framework.txt
@@ -695,3 +695,40 @@ The better way to understand it is to take a look at vivi driver. One
 of the main reasons for vivi is to be a videobuf usage example. the
 vivi_thread_tick() does the task that the IRQ callback would do on PCI
 drivers (or the irq callback on USB).
+
+struct v4l2_fh
+--------------
+
+struct v4l2_fh provides a way to easily keep file handle specific data
+that is used by the V4L2 framework.
+
+struct v4l2_fh is allocated as a part of the driver's own file handle
+structure and is set to file->private_data in the driver's open
+function by the driver. Drivers can extract their own file handle
+structure by using the container_of macro.
+
+Useful functions:
+
+- v4l2_fh_init()
+
+  Initialise the file handle. This *MUST* be performed in the driver's
+  v4l2_file_operations->open() handler.
+
+- v4l2_fh_add()
+
+  Add a v4l2_fh to video_device file handle list. May be called after
+  initialising the file handle.
+
+- v4l2_fh_del()
+
+  Unassociate the file handle from video_device(). The file handle
+  exit function may now be called.
+
+- v4l2_fh_exit()
+
+  Uninitialise the file handle. After uninitialisation the v4l2_fh
+  memory can be freed.
+
+The users of v4l2_fh know whether a driver uses v4l2_fh as its
+file->private_data pointer by testing the V4L2_FL_USES_V4L2_FH bit in
+video_device->flags.
-- 
1.5.6.5

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