Re: [v3,11/41] mips: reuse asm-generic/barrier.h

From: Peter Zijlstra
Date: Tue Jan 12 2016 - 05:26:46 EST

On Tue, Jan 12, 2016 at 10:27:11AM +0100, Peter Zijlstra wrote:
> 2) the changelog _completely_ fails to explain the sync 0x11 and sync
> 0x12 semantics nor does it provide a publicly accessible link to
> documentation that does.

Ralf pointed me at:

> 3) it really should have explained what you did with
> smp_llsc_mb/smp_mb__before_llsc() in _detail_.

And reading the MIPS64 v6.04 instruction set manual, I think 0x11/0x12
are _NOT_ transitive and therefore cannot be used to implement the
smp_mb__{before,after} stuff.

That is, in MIPS speak, those SYNC types are Ordering Barriers, not
Completion Barriers. They need not be globally performed.