RFC: ARM Boot standard for passing device tree blob

[linux@arm.linux.org.uk (Russell King - ARM Linux)]

On Fri, Mar 26, 2010 at 01:52:24PM -0600, Grant Likely wrote:
> I could change the statement to something like, "virtually tagged or
> indexed data cache(s) must be off", or drop the statement entirely
> since it is implied by the requirement that the MMU must be off.

1. We're not going down the path of having differing conditions for
   different caches; to do so would mean that we'd need to have two
   entirely different sets of code to handle booting in the kernel.

2. No ARM CPU supports having the D-cache enabled without the MMU; the
   data cache needs to be told via the page tables what can be cached
   and what can't - it needs to be told that RAM can cached but IO
   devices must not be.

In short, the MMU must always be off, which in turn means the D-cache
must always be disabled.