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Date: Tue, 27 Mar 2018 15:36:29 +0100
From: Will Deacon <will.deacon@arm.com>
To: Sinan Kaya <okaya@codeaurora.org>
Cc: Arnd Bergmann <arnd@arndb.de>,
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Subject: Re: RFC on writel and writel_relaxed
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On Tue, Mar 27, 2018 at 09:46:51AM -0400, Sinan Kaya wrote:
> On 3/27/2018 7:02 AM, Will Deacon wrote:
> > -     See Documentation/DMA-API.txt for more information on consistent memory.
> > +     can see it now has ownership.  Note that, when using writel(), a prior
> > +     wmb() is not needed to guarantee that the cache coherent memory writes
> > +     have completed before writing to the MMIO region.  The cheaper
> > +     writel_relaxed() does not provide this guarantee and must not be used
> > +     here.
> 
> Can we say the same thing for iowrite32() and iowrite32be(). I also see wmb()
> in front of these.

I don't think so. My reading of memory-barriers.txt says that writeX might
expand to outX, and outX is not ordered with respect to other types of
memory.

Will