+ * At this point we don't know whether the cache is enabled or not - a
+ * bootloader may have enabled it. There are at least 2 things that
+ * could be dirty in the cache at this point:
+ * 1. kernel command line set up by boot loader
+ * 2. spilled registers from the prolog of this function
+ * => before re-initialising the cache, we must do a purge of the whole
+ * cache out to memory for safety. As long as nothing is spilled
+ * during the loop to lines that have already been done, this is safe.
+ * - RPC