[PATCH 3/3] Documentation: add doc for sync_file_get_fence()

[Gustavo Padovan <gustavo@padovan.org>]

From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>

Document the new function added to sync_file.c

v2: Adapt to fence_array

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
---
 Documentation/sync_file.txt | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/Documentation/sync_file.txt b/Documentation/sync_file.txt
index eaf8297..46f5769 100644
--- a/Documentation/sync_file.txt
+++ b/Documentation/sync_file.txt
@@ -64,6 +64,25 @@ The sync_file fd now can be sent to userspace.
 If the creation process fail, or the sync_file needs to be released by any
 other reason fput(sync_file->file) should be used.
 
+Receiving Sync Files from Userspace
+-----------------------------------
+
+When userspace needs to send an in-fence to the driver it pass file descriptor
+of the Sync File to the kernel. The kernel then can retrieve the sync_file
+from it.
+
+Interface:
+	struct fence *sync_file_get_fence(int fd);
+
+
+The function return a struct fence pointer referencing the fence(s) in the Sync
+File. If the Sync File contains only one fence, this fence is returned. But if
+has more than one fence a fence_array[3] is returned. However the callers only
+see the arrays' base class which is struct fence. In both cases a reference to
+the returned fence is held.
+
+
 References:
 [1] struct sync_file in include/linux/sync_file.h
 [2] All interfaces mentioned above defined in include/linux/sync_file.h
+[1] struct fence_array in include/linux/fence-array.h
-- 
2.5.5