[U-Boot] [PATCH] ARM926: Add mb to the cache invalidate/flush

Albert ARIBAUD
2012-10-11T22:44:53Z

Hi Scott,

On Thu, 11 Oct 2012 16:09:28 -0500, Scott Wood
<scottwood@freescale.com> wrote:

> On 10/11/2012 03:01:32 PM, Albert ARIBAUD wrote:
> > Hi Mark,
> >
> > Thanks for your example.
> >
> > > My understanding of gcc is that global memory accesses are meant to
> > > stay on the correct side of an asm with a "memory" clobber. The gcc
> > > manual states that if you use a memory clobber, the asm should also
> > > be volatile.
> >
> > Not exactly. It states that you need to add volatile if you cannot
> > tell
> > where in memory your instruction will write; if you can tell (by
> > specifying "m" as an output of the asm) then volatile is not
> > needed -- simply because the compiler can tell where in memory the
> > write will happen, and will thus not eliminate the asm statement as
> > long as the destination memory is not optimized out.
>
> You're confusing the part about adding volatile to the asm statement to
> keep it from being completely removed, from anything to do with
> ordering or clobbers.

*Please* stop pretending I am saying things I haven't.

All I said in the above answer is that contrary to what Mark said about
the doc, it does not require adding volatile to memory clobbers: 'You
will also want to add the volatile keyword if the memory affected is
not listed in the inputs or outputs of the asm, as the `memory' clobber
does not count as a side-effect of the asm'.

*Nowhere* in my answer above did I state anything related to ordering.

> -Scott

Amicalement,
--
Albert.