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SubjectRe: [PATCH 0/24] make atomic_read() behave consistently across all architectures
>>>> And no, RMW on MMIO isn't "problematic" at all, either.
>>>> An RMW op is a read op, a modify op, and a write op, all rolled
>>>> into one opcode. But three actual operations.
>>> Maybe for some CPUs, but not all. ARM for instance can't use the
>>> load exclusive and store exclusive instructions to MMIO space.
>> Sure, your CPU doesn't have RMW instructions -- how to emulate
>> those if you don't have them is a totally different thing.
> Let me say it more clearly: On ARM, it is impossible to perform atomic
> operations on MMIO space.

It's all completely beside the point, see the other subthread, but...

Yeah, you can't do LL/SC to MMIO space; ARM isn't alone in that.
You could still implement atomic operations on MMIO space by taking
a lock elsewhere, in normal cacheable memory space. Why you would
do this is a separate question, you probably don't want it :-)


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