media: videobuf2-core.h: Document the alloc memop size argument as page aligned

The size argument of the alloc memop, which allocates buffer memory, is
page aligned. Document it as such in the only caller as well as ops
documentation.
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

drivers/media/common/videobuf2/videobuf2-core.c

@@ -205,6 +205,7 @@ static int __vb2_buf_mem_alloc(struct vb2_buffer *vb)
 	 * NOTE: mmapped areas should be page aligned
 	 */
 	for (plane = 0; plane < vb->num_planes; ++plane) {
+		/* Memops alloc requires size to be page aligned. */
 		unsigned long size = PAGE_ALIGN(vb->planes[plane].length);
 
 		/* Did it wrap around? */

include/media/videobuf2-core.h

@@ -54,7 +54,8 @@ struct vb2_threadio_data;
  *		will then be passed as @buf_priv argument to other ops in this
  *		structure. Additional gfp_flags to use when allocating the
  *		are also passed to this operation. These flags are from the
- *		gfp_flags field of vb2_queue.
+ *		gfp_flags field of vb2_queue. The size argument to this function
+ *		shall be *page aligned*.
  * @put:	inform the allocator that the buffer will no longer be used;
  *		usually will result in the allocator freeing the buffer (if
  *		no other users of this buffer are present); the @buf_priv