On Sat, 2009-11-28 at 21:43 +0100, Albert Herranz wrote:

+        * Prepare again the same BAT for MMU_init.
+        * This allows udbg I/O to continue working after the MMU is
+        * turned on for real.
+        *
+        * We are assuming here that exi_io_base is identity mapped.
+        */
+       addr = ((unsigned long)exi_io_base) & 0xffff0000;
+       setbat(1, addr, addr, 128*1024, PAGE_KERNEL_NCG); 

How do you prevent that from overlapping otherwise valid kernel
mappings ?

You need to allocate the virtual space. For a debug thing like that, you
could use the fixmap. In fact, I think we should create a fixmap entry
or two always available for use by early debug.

Cheers,
Ben.