[RFC] arm: Defer lookup of machine_type and vet of atags to setup.c

On Wed, Jan 12, 2011 at 09:24:34AM -0700, Grant Likely wrote:

Actually it looks like the real problem is that the mmu has been
turned on, but the virtual mappings for devices have not yet been
established, and so the debug macros aren't using a valid address.

They should be, as they're valid for use from assembly prior to MMU
turn-on, assembly after MMU turn-on and C code.

If CONFIG_DEBUG_LL is enabled, create_page_tables() should be setting
up the necessary initial mappings for printascii() to work.

Maybe the efforts to unify that stuff ended up breaking the printascii
debugging mechanism, and we now require a new debugging mechanism to
debug the printascii debugging mechanism... :-P

I've used it on Versatile Express during the last week and it did work
right from before setup_arch() was called.

It looks like I'd need to get past paging_init() in order to get
ll_debug working between turning on the mmu and paging_init(), but
paging_init() needs the mdesc pointer, and the whole point of the
error message is that the mdesc pointer is unknown!  I don't see any
code that sets up a debug mapping of the uart before paging_init time.

See the #ifdef CONFIG_DEBUG_LL section in create_page_tables in head.S