[U-Boot] [PATCH 3/9] arm: Move CP15 init out of cpu_init_crit()

[Albert ARIBAUD <albert.u.boot@aribaud.net>]

Hi Simon et al.,

Thanks to you and others for their patience. Let me summarize the thread:

- ARM7TDMI definitely lacks a cp15, as AN99 explicitely states;

- ARM provides no other, reliable, way to identify an ARM7TDMI reliably;

- Identification through a manufacturer-specific method just defeats the 
goal.

This makes it impossible to support ARM7TDMI (as well as others listed 
in AM99)  with a start.S code that contains cp15 instructions.

OTOH, I've gone through a number of ARM TRMs for cores that have 
caches/MMU and they all state that these are disabled on reset. I will 
also assume that when U-Boot starts indirectly through SPL or any other 
mechanism, and if this mechanism uses caches/MMU, then it will disable 
them properly before passing control to U-Boot, just like U-Boot 
disables caches etc before passing control to e.g. Linux.

I understand that this initialization is done so that the the cache/MMU 
is in a correct state, and this must still be ensured, but I now think 
that ensuring this is the burden of whatever passed control to the start 
label (this includes true resets, branching from SPL or any other IPL, 
and --ugh-- branching to start from inside U-Boot).

Based on this, I revise my opinion that the caches and MMU cleaning code 
in start.S should be kept there, and actually I now consider that they 
should be removed entirely.

However, removing cp15 inits would mean a *third* revision of your 
patchset, plus it could cause unexpected issues which I don't want to 
happen at this point of the release cycle.

Therefore, I'll go back to your patch as posted on oct 13th.

Apologies for the long discussion.

Amicalement,
-- 
Albert.