+ * coherent_user_range(start, end)
+ *
+ * Ensure coherency between the Icache and the Dcache in the
+ * region described by start, end. If you have non-snooping
+ * Harvard caches, you need to implement this function.
+ * - start - virtual start address
+ * - end - virtual end address
+ *
+ * flush_kern_dcache_area(kaddr, size)
+ *
+ * Ensure that the data held in page is written back.
+ * - kaddr - page address
+ * - size - region size
+ *