On Wed, Mar 28, 2018 at 08:29:45AM +1100, Benjamin Herrenschmidt wrote:

On Tue, 2018-03-27 at 15:36 +0100, Will Deacon wrote:

quoted

quoted

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.

Ugh ?

My understanding of HW at least is the exact opposite. outX is *more*
ordered if anything, than any other accessors. IO space is completely
synchronous, non posted and ordered afaik.

I'm just going by memory-barriers.txt:


 (*) inX(), outX():

     [...]

     They are guaranteed to be fully ordered with respect to each other.

     They are not guaranteed to be fully ordered with respect to other types of
     memory and I/O operation.


For arm/arm64 these end up behaving exactly the same as readX/writeX, but
I'm nervous about changing the documentation without understanding why it's
like it is currently. Maybe another ia64 thing?.

Will