gallium: comments for surface_copy(), surface_fill() in p_context.h

src/gallium/include/pipe/p_context.h

@@ -192,14 +192,21 @@ struct pipe_context {
     * Surface functions
     */
    /*@{*/
+
+   /**
+    * Copy a block of pixels from one surface to another.
+    * The surfaces must be of the same format.
+    */
    void (*surface_copy)(struct pipe_context *pipe,
 			struct pipe_surface *dest,
 			unsigned destx, unsigned desty,
-			struct pipe_surface *src, /* don't make this const - 
-						     need to map/unmap */
+			struct pipe_surface *src,
 			unsigned srcx, unsigned srcy,
 			unsigned width, unsigned height);
 
+   /**
+    * Fill a region of a surface with a constant value.
+    */
    void (*surface_fill)(struct pipe_context *pipe,
 			struct pipe_surface *dst,
 			unsigned dstx, unsigned dsty,