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

On Wed, 12 Jan 2011, 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.

A temporary virtual mapping should be there -- look for addruart in 
head.S.

I'm using printk to get output into the ring buffer in my patch to
rework lookup_machine_type() in C, and that does indeed output to the
ring buffer, but the kernel cannot spit stuff out the serial port.

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 above.

 I could try to implement something like that, but it is looking to be
more complicated than it is worth when the current code works just
fine.

My bet is that there is a bug with the current code that you are 
exposing.

Let me know if I've missed something, but I think I should drop the
removal of __lookup_machine_type from head.S from my patch.

It's not the location of that code which is a problem.  Even if you 
leave that code in place, you want to call it later and I bet that the 
display would be broken even if __lookup_machine_type doesn't move.


Nicolas