Moan: usage of __iormb() and __iowmb() outside of asm/io.h

Russell King - ARM Linux linux at
Wed Jun 10 04:24:34 PDT 2015

On Wed, Jun 10, 2015 at 12:18:20PM +0100, Will Deacon wrote:
> Hi Russell,
> On Mon, Jun 08, 2015 at 07:47:01PM +0100, Russell King - ARM Linux wrote:
> > I notice that we have users of __iormb() and __iowmb() outside of asm/io.h:
> > 
> > drivers/clocksource/timer-keystone.c:   __iowmb();
> > drivers/dma/cppi41.c:                   __iormb();
> > drivers/dma/cppi41.c:   __iowmb();
> > drivers/dma/cppi41.c:           __iowmb();
> > drivers/dma/cppi41.c:                   __iormb();
> > drivers/soc/ti/knav_qmss_queue.c:       __iowmb();
> > 
> > These are not official kernel barriers - the only reason they exist in
> > asm/io.h is purely to provide a barrier implementation _for_ creating
> > the accessors _in_ asm/io.h, which are macros, and therefore these
> > macros need to stay around for the same scope as those accessors.
> > 
> > As with all details which are an architecture matter, they are subject
> > to the whims of the architecture maintainer to provide whatever semantics
> > for them that the architecture maintainer deems fit: there is no official
> > requirement for anything of that nature to do anything, and no guarantee
> > that anything such a detail does today it will do so tomorrow.
> > 
> > This is why only official interfaces should be used, and if they do not
> > satisfy the requirements, then new official interfaces need to be 
> > proposed.  Don't ever poke about with stuff that's an architecture
> > implementation detail.
> > 
> > We've been here before with some of the cache flushing code - and people
> > have been burnt by it.
> > 
> > I do wish that people would see the difference between stuff which is
> > implemented to facilitate the implementation of an architecture detail
> > vs something which is provided for everyone's use.
> > 
> > I'm working on a patch which will completely remove these from view.
> > I would strongly suggest that these uses are removed from the above
> > code as a matter of urgency.
> I agree to removing these from view; we already have plenty of barrier
> macros and we don't want these to proliferate outside of the arch code.
> Any chance you could do a similar change for arm64, please (we have the
> same macros there)?

Yes - as you're aware, removing them from sight does cause us to decend
into macro-hell in asm/io.h, but I think that's better than having people
get their grubby fingers on arch internal stuff they shouldn't be touching.

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