dma-buf: Update [un]map documentation to match the other functions

Other function have inline documentation, a couple still have
theirs at the top of the structure, update the docs and move
them inline.
Signed-off-by: Andrew F. Davis <afd@ti.com>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190321200957.16938-2-afd@ti.com

include/linux/dma-buf.h

@@ -39,8 +39,6 @@ struct dma_buf_attachment;
 
 /**
  * struct dma_buf_ops - operations possible on struct dma_buf
- * @map: [optional] maps a page from the buffer into kernel address space.
- * @unmap: [optional] unmaps a page from the buffer.
  * @vmap: [optional] creates a virtual mapping for the buffer into kernel
  *	  address space. Same restrictions as for vmap and friends apply.
  * @vunmap: [optional] unmaps a vmap from the buffer
@@ -200,8 +198,6 @@ struct dma_buf_ops {
 	 * to be restarted.
 	 */
 	int (*end_cpu_access)(struct dma_buf *, enum dma_data_direction);
-	void *(*map)(struct dma_buf *, unsigned long);
-	void (*unmap)(struct dma_buf *, unsigned long, void *);
 
 	/**
 	 * @mmap:
@@ -240,6 +236,31 @@ struct dma_buf_ops {
 	 */
 	int (*mmap)(struct dma_buf *, struct vm_area_struct *vma);
 
+	/**
+	 * @map:
+	 *
+	 * Maps a page from the buffer into kernel address space. The page is
+	 * specified by offset into the buffer in PAGE_SIZE units.
+	 *
+	 * This callback is optional.
+	 *
+	 * Returns:
+	 *
+	 * Virtual address pointer where requested page can be accessed. NULL
+	 * on error or when this function is unimplemented by the exporter.
+	 */
+	void *(*map)(struct dma_buf *, unsigned long);
+
+	/**
+	 * @unmap:
+	 *
+	 * Unmaps a page from the buffer. Page offset and address pointer should
+	 * be the same as the one passed to and returned by matching call to map.
+	 *
+	 * This callback is optional.
+	 */
+	void (*unmap)(struct dma_buf *, unsigned long, void *);
+
 	void *(*vmap)(struct dma_buf *);
 	void (*vunmap)(struct dma_buf *, void *vaddr);
 };