From: Jesse Barnes <jbarnes@engr.sgi.com>
To: Albert Cahalan <albert@users.sourceforge.net>
Subject: Re: [PATCH] I/O space write barrier
Date: Mon, 4 Oct 2004 14:20:01 -0700
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On Monday, October 4, 2004 1:39 pm, Albert Cahalan wrote:
> > diff -Nru a/include/asm-ppc/io.h b/include/asm-ppc/io.h
> > --- a/include/asm-ppc/io.h 2004-09-27 10:48:41 -07:00
> > +++ b/include/asm-ppc/io.h 2004-09-27 10:48:41 -07:00
> > @@ -197,6 +197,8 @@
> >  #define memcpy_fromio(a,b,c)   memcpy((a),(void *)(b),(c))
> >  #define memcpy_toio(a,b,c) memcpy((void *)(a),(b),(c))
> >
> > +#define mmiowb() asm volatile ("eieio" ::: "memory")
> > +
> >  /*
> >   * Map in an area of physical address space, for accessing
> >   * I/O devices etc.
>
> I don't think this is right. For ppc, eieio is
> already included as part of the assembly for the
> IO operations. If you could delete that, great,
> but I suspect that nearly all drivers would break.

Ok, if it's covered than mmiowb() can just be empty for ppc.

> BTW, the "eieio" name is better. The "wb" part
> of "mmiowb" looks like "write back" to me, as if
> it were some sort of cache push operation. It is
> also lacking an appropriate song. :-)

It's supposed to be 'write barrier' just like wmb is a write memory barrier, 
so is mmiowb a memory-mapped I/O write barrier.  Make sense?

Thanks,
Jesse
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