Re: [PATCH] Orion NAND: Make dword load asm volatile to avoid GCC optimizing it away

[Simon Kagstrom <simon.kagstrom@netinsight.net>]

On Thu, 20 Aug 2009 12:14:47 -0400 (EDT)
Nicolas Pitre <nico@cam.org> wrote:

> > Yes, it works fine with 4.3.3 and 4.4.1 with this change. So the
> > updated patch can be found below. I belive the early clobber should be
> > there though, since (from the ARM architecture reference manual):
> > 
> >   If <addressing_mode> performs base register write-back and the base
> >   register <Rn> is one of the two destination registers of the
> >   instruction, the results are UNPREDICTABLE.
> > 
> > it works fine without the early clobber as well, but I'd feel more safe
> > having it in.
> 
> But this isn't the case here.  We don't perform any writeback.
> You get a writeback when you have an addressing mode of the form:
> 
> 	insn	rd, [rn, rm]!
> 	insn	rd, [rn, #off]!
> 	insn	rd, [rn], #off
> 
> but not with:
> 
> 	insn	rd, [rn, #off]

OK, I'm still a beginner on the ARM architecture, so thanks for the
explanation!

> Still the early clobber shouldn't have any adverse effect either, unlike 
> the memory clobber.
> 
> Acked-by: Nicolas Pitre <nico@marvell.com>
> 
> Unless the MTD guys are going to pick this patch and push it to Linus 
> soon I'll carry it in the Orion git repo.

Great, thanks!

// Simon