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

santosh shilimkar santosh.shilimkar at
Wed Jun 10 10:25:54 PDT 2015

On 6/10/2015 3:59 AM, Murali Karicheri wrote:
> On 06/08/2015 02:47 PM, Russell King - ARM Linux wrote:
>> Guys,
>> 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();
Looks like CPPI abuse got carry forwarded. I also missed these because
of oversight. Should have insisted to use the standard accessors.

>> 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.
Sorry for that Russell and thanks for addressing it advance.


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