cachepolicy on arm UP/SMP

[Catalin Marinas]

2011/4/2 rocky <bill_carson at 126.com>:
> I am a little confused about arm cachepolicy for UP/SMP.
>
> in arch/arm/mm/mmu.c
> for UP , default cache policy is CPOLICY_WRITEBACK;
> while for SMP, cache policy is overrided with  WRITEALLOC.
>
> why does SMP cannot use WRITEBACK?
> It is about coherency issue?

Historical reasons I think because ARM11MPCore only supported WBWA
caches, though even if only WB configuration was set.

Note that WB or WBWA is just a hint and the processor is allowed to do
write allocation or ignore it. We could simply make both the same at
least on ARMv6+ hardware (and I'm more in favour of WBWA).

-- 
Catalin