media: vb2-core: vb2_ops: document non-interrupt-context calling

Driver writers can benefit in knowing if/when callbacks are called in
interrupt context. But it is not completely obvious here, so document
it.
Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Pawel Osciak <pawel@osciak.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

include/media/videobuf2-core.h

@@ -296,6 +296,9 @@ struct vb2_buffer {
 /**
  * struct vb2_ops - driver-specific callbacks.
  *
+ * These operations are not called from interrupt context except where
+ * mentioned specifically.
+ *
  * @queue_setup:	called from VIDIOC_REQBUFS() and VIDIOC_CREATE_BUFS()
  *			handlers before memory allocation. It can be called
  *			twice: if the original number of requested buffers